We've seen some amazing TV prices on Black Friday. Big 4K TVs, probably HDR, for lower prices than ever.

Walmart is selling a 40-inch TV for $100. Target has a 55-incher for $200. Best Buy is selling a massive 70-inch TV for $700. And that's just the beginning.

The prices sure are impressive, but that doesn't mean the TVs will be a good value.

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Quite often cheap TVs are just that: cheap. Low-cost sets without the features or image quality of their more-expensive competition might seem like a bargain, but aren't actually a good place to invest your money. After all, most people keep their TVs for 5 or 10 years.

The low prices on these TVs should make you more cautious, not less. Approach these TV sales with a careful eye, separate from the price.

That's why CNET's list of Black Friday 2018 TV deals is divided into two parts: the best and the cheapest. The first part covers TV where our reviewer, David Katzmaier, can vouch for the picture quality and they're great bargains. The second covers TVs he didn't test, but he's guessing they won't hold a candle to the image quality of the ones he recommends.

With that difference in mind, here are a few things to look for when evaluating that temptingly priced TV.

Beware: 'Fake' HDR

Fake high dynamic range (HDR) is one of the biggest issues in the TV world right now. Being able to read HDR and properly display HDR are two hugely different things. It's easy for a TV to read HDR metadata and therefore claim it's "HDR compatible." But without local dimming there's no way for the TV to show that HDR data. In essence, this is like someone reading you a description of a painting. You'll get the idea, but you're not going to see it.

For more information about this marketing lie, read this: Why all HDR on TVs isn't the same.

Beware: Fake refresh rates

With LCD TVs, higher refresh rates can reduce the perception of motion blur, as in the blurring when anything moves on screen. This is an issue with all LCD TVs, and the current versions of OLED. However, not everyone sees it or is bothered by it.

The problem is most manufacturers are a bit, shall we say, "creative" with their listings for refresh rate. They might say "Motion rate 120" or "SRR240Hz" or some other marketing term to describe what their TV is doing. Many of these aren't actually a higher refresh rate. They're merely processing tricks, or if you're lucky, black frame insertion (which can be good in some cases). If it's a cheap TV, it's almost assuredly not actually 100 or 120Hz, which means fast motion will be blurred.

For more info, check out the truth about Ultra HD 4K TV refresh rates.

Beware: Sparse connections

How many HDMI connections do you need? More importantly, how many Ultra HD HDMI connections do you need? If you have more than one source that's 4K, make sure every input on your TV is HDMI 2.0 or greater, and has HDCP 2.2. If you can't find this info on the spec sheet, be wary. If the connection doesn't have HDCP 2.2, you won't be able to watch a 4K source.

Beware: Not-so-smart TV

For the most part, the major TV companies and brands like Roku have the whole smart TV thing down solid. Off brands might not. This isn't a huge deal, as media streamers are inexpensive and great, but if you're expecting a quality streaming experience, you might not get it. You also might not get all the streaming services you want. Everything has Netflix, not everything has Amazon, Vudu, Hulu and so on. TVs with Chromecast built-in, for example, require you to use your phone, and don't always stream Amazon video.

Sarah Tew/CNET

Beware: Shopping by brand only

There are several lesser-known brands that are making fantastic TVs. TCL is a recent standout. So just because they're not as well known as, say, Samsung or Sony, that doesn't necessarily mean you should cross them off your list. That said, an unknown brand may not have the same warranty or repair support, if needed.

During Black Friday well-known name brands like Samsung and LG often sell their cheapest models for prices far below what you may expect. A lot are fine, but some might not deliver the same level of picture quality or features as a lesser-known brand like TCL or Vizio -- both of which routinely top CNET's list of best TVs for the money. In other words, even on Black Friday a TV's brand shouldn't be the sole determining factor.

And on the flip side, there are many brands that you might recognize that are nothing but the name of a formerly great company. Chinese companies have spent years buying up the trademarks of once-storied companies. Polaroid, Kodak and many others have little to no relation to the companies you once knew. They're Chinese manufacturers looking to use the name recognition of a once-great brand. Again, these aren't necessarily bad, but don't let the name fool you.

But if you insist…

Here's the thing: If you're just looking for a cheap TV for a second room, sure, why not? If you really don't care what the TV looks like, sure, why not? But if you're excited about new TV features like HDR, wide color gamut and so on, you might be disappointed.

Black Friday deals: See every Black Friday 2018 deal we've found so far.

Holiday Gift Guide: CNET's full gift guide, including dozens of products priced under $25, $50 and $100.

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the same, TV resolutions explained, LED LCD vs. OLED and more.

Still have a question? Tweet at him @TechWriterGeoff, then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel and its sequel.