Some customers like to take advantage of stores' return policies by making rather unusual returns.

Business Insider spoke to employees at Costco, Walmart, Target, and Home Depot about the oddest returns they've ever witnessed.

Employees described encountering shoppers who returned things like dirty toilets and mostly consumed pies.

Some shoppers like to take advantage of major retailers' return policies.

But then there are customers who take that impulse to a whole new level. The rise of "serial returners" is costing the industry a fortune and causing major logistical headaches.

To get a sense of what this looks like at the store level, Business Insider spoke to employees at Walmart, Target, Costco, and Home Depot about the strangest, grossest, and most surprising returns they've seen on the job.

Some of their responses were out there.

"We can't say no to any members, so don't bring anything back that's 10 years old, such as a fake Christmas tree we got back that was sold in 2007," a California-based Costco employee previously told Business Insider. "We want to help, but that sets a bad example for everyone to bring anything back."

Meanwhile, a Target team member based in California told Business Insider that they admired their colleagues working in returns, describing it as "a very tough position."

Here are some of the most ridiculous returns that retail workers said they'd seen.