For more than a decade, the big-screen TV has ranked near the top of the most coveted bargains on Black Friday. But can these video doorbusters sometimes be duds?

“Absolutely,” said Randy Thompson, lead technician at ShopJimmy in Burnsville, a distributor of TV parts and accessories.

There are many good TV deals from Thanksgiving to Cyber Monday, but consumers should look for some red flags.

Entry-level TVs can suffer from poor sound and picture quality, a poorly designed remote control and a lack of support for service issues after the sale, Thompson said. Some may need a sound bar, a speaker designed to fit underneath the TV, to boost volume. For others, the replacement parts needed if the TV has a problem may be available for only a short time.

TV prices drop as new technology replaces the old, but sometimes it makes sense to spend more for better features and performance. Lindsay Sakraida, director of content marketing with DealNews said TV buyers this year should look for 4K screen resolution which doesn’t cost much more than the 1080p resolution that for many years was the best available for HDTVs.

“4K is much better and may only cost $20 more,” she said. “It’s a more advanced, nearly future-proof TV.”

Many of the screens for Black Friday are known as “derivative” or one-off TVs made specifically for the event. The quality may be substandard, but manufacturers and retailers can disguise it by not providing a model number. Without that, consumers are unable to search price history or reviews. Even when manufacturers provide a model number, consumers who can’t find any reviews online can usually assume it’s a derivative.

Best Buy prefers to use brand names, spokeswoman Paula Baldwin said. “We know our customers don’t just want a great deal, they want a great deal on the brands they trust and love,” she said via e-mail. “This is why you’ll see trusted brands like Sony, Samsung and Sharp on the front cover of our Black Friday ad.”

Manufacturers will sometimes take a highly regarded existing model, put in some lower-cost parts or trim some inputs and give it a different model number.

“A retailer may sell a slightly different product than in the ad,” Thompson said. “Manufacturers like Samsung, Element and Westinghouse can make up to 10 versions of the same TV.”

Consumers can find TVs of varying quality at any retailer, but they should look twice at retailers that only sell TVs during the holidays, such as hardware stores. “It varies from year to year, but Kohl’s has some good deals this year,” Sakraida said.

To find out how good of a deal a certain TV may be, experts suggest looking beyond the suggested retail price in the ads. Search for other prices online or use a price history tool such as Camelcamelcamel. It can track prices for a future purchase as well as price history charts.

Also check Consumer Reports for ratings and manufacturer reliability.

Once the doorbuster is in the house, keep the packaging and run the TV as much as possible while it can still be returned to the store for a full refund. That’s usually 14 to 90 days, depending on the retailer. Make sure the streaming and the HDMI ports work and that there are no spots on the screen.

“And turn the sound up and listen for rattles,” Thompson said. “That’s a common problem with cheap TVs.”