If you stalk the real estate listings in your neighborhood and make the open house rounds on the weekends you may feel pretty good about your real estate knowledge. I know I like to play the game of guessing my home's value every time a house near us sells. But real estate can be a high stakes game, even if it sometimes seems like play money being thrown around on real estate TV shows. A misstep can cost thousands, even tens of thousands of dollars, but how do you even know what you don't know?

To get some insight into mistakes many of us may be making when it comes to our houses, I talked with Seattle-based real estate expert Aaron Hendon. And did he set me straight.

Here are the six top things we're getting wrong about real estate.

1. You trust an algorithm knows your home's value

The worst thing Hendon sees, he told NBC News BETTER, is homeowners who assume they know something about the value of a house. Maybe they saw something about real estate prices on the news, or talked to their uncle, or saw it on Zillow, he said. The absolute worst, he added, is to think that the Zestimate is the true value of your home.

The “Zestimate” is an estimated value listed on popular real estate site Zillow. And it's notoriously off, Hendon said. So badly so, in fact, that when Zillow CEO Spencer Rascoff sold his condo, the the Zestimate was 40 percent off.

“The problem is you can't do it by an algorithm because there are too many variables and they change too rapidly to get a good read,” Hendon explained. “The assumption is there's a real inherent value to our house but there is not. There's what a buyer is willing to pay for it on the day they buy it and what the seller is willing to take for it. You're selling a commodity, one of multiple houses, and you have no idea who's shopping that particular week. How could you value your house by a computer estimate? At best it's a guess.”

But “it's a shiny website and looks like it has authority,” he said. “It's a real problem that people tend to weight those things heavily.”

There is some value to be found in the Zestimate, however, Hendon said. “Say I want to track my house value over time. I check the Zestimate every six months, and it's going up. It doesn't tell me what it's worth but tells me it's worth more than it was.”

2. You think your neighbor's house will tell you your home's value

So the house up the street just sold. You quickly do the math and figure out the price per square foot, then apply that to yours: voila, there's your value.

Not so fast.

“The problem with that logic is you don't really know the details of the house that sold,” Hendon said, “the particular way it was marketed, maybe the realtor did crappy pictures or maybe the owner took out loan after loan so they're under water. They don't know the conditions upon which, or to whom it was sold, or the terms.” It could have sold for cash, the owner could have been leaving the country or going through a divorce, and that's not even to mention the huge variance possible in the condition of the house.

What's more, “all square footage is not equal,” he said. If it were, “that would mean 4000 square feet should be worth twice as much as 2000. You need a first thousand to even have a house, the next thousands are options. What are those rooms? Bedrooms are worth way less than bathrooms.” People tend to gloss over a myriad of variables that are hidden, he said.

3. You believe the appraiser sets the value

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“The tendency is to live like the appraiser is coming up with the true value,” Hendon said. But, he reiterated, “there is no value, it doesn't exist, it's worth what someone will pay for it and you'll accept.”

At the end of the day “it's a subjective valuation of your property,” he said. The appraiser doesn't have to agree that you paid the right amount. “Their job in that case is to say to the bank, 'if this guy defaults you'll be able to get your money back.'”

While a common worry during homebuying and selling is that the house won't appraise for the sale price, “rarely does it not come in at value,” he said. “By definition if you're willing to pay it, it's worth it. Why would you pay for it if it wasn't?”

This, at least, is one thing not to worry so much about.

4. You think renovating before selling will boost the value

Tempted to upgrade the kitchen or get new carpet right before you sell? That's a mistake, Hendon said. “Don't redo your house right before you sell. I can't tell you the number of people I have to talk out of remodeling right before sale. I'm a little blunt, I go 'that's crazy thinking.'”

He asks sellers to look at the math. “You're going to spend how much to redo kitchen? Say 15? Do you think we'll get 20 more? The kitchen will be torn up for six months, that's got to be worth something, and then we don't know what the market will be in six months — and everyone may not love your choices.”

When's the right time to remodel? Five years ago, Hendon said.

“If you did it five years ago and you loved it and used it you don't care if you get the money back.”

If you're a professional flipper, go for it, he said. Otherwise, “clean it, get it neutral. You'll get less, but the net will be the same.” And you save yourself the hassle.

5. You underestimate the role of the realtor

Homes are the most expensive, most emotionally impactful, rarest sale and purchase in our lives, Hendon said. “What makes me craziest — when people go hire a realtor, they do it with due diligence of where to eat dinner. They hire their friend, they go to Yelp or Zillow and see stars, they use a discount broker or see a guy's signs all over the neighborhood.”

“None of it has anything to do with performance,” he said. “Sure go try the Chinese restaurant your friend recommends, but using your uncle's realtor without asking them to show you how much they sell houses for compared to asking price, you're crazy.”

“No one has ever asked me to see my last 12 months statistics,” he said. “That is crazy to me.

It takes nothing to ask that.” And no realtor should be offended by the question, he said. “You're going to give someone $8,000 [commission] they should be ready to compete, they should be ready to fight for your business.”

6. You can save the six percent by selling the house yourself

While in a very hot market there could be value in a FSBO, or for sale by owner, the math on this rarely pans out, Hendon said.

First, it's not six percent, because almost every buyer will have realtor, he said, “so they still have to spend that three percent [for the buyer's agent].” So you're down to three percent. Which is still a lot of money.

Is it worth it? “If you don't have a job [so you have the time], and you're ok with letting strangers in your house and leaving while they're there, and doing all the work, and will somehow find a way to price it correctly, and don't mind the risk involved in the liability of getting it to close, and you who do not negotiate for a living, who do not sell a hundred houses a year are going to trust that the buyer's agent is somehow not going to screw you over ...” Hendon said. We'll take that as a you do the math.

When my husband and I sold our last house and bought our current one, some of the biggest value to us was our realtor's role as counselor in guiding us through the process and keeping our best interests first in negotiations with our buyer and seller and their respective agents. It felt like a house of cards most days that would fall apart at any moment, but he made it happen and that was more than worth the commission.

We also listed and sold our house for more than we'd have ever tried ourselves. Hendon wasn't surprised to hear this.

The trouble with selling your own home, he said, is “most people make it look like a yard sale. The same sign from Home Depot that says 'yard sale' but it says 'home for sale.' No one goes to a yard sale and pays full price, it's a yard sale for God's sake.”

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