It's an online vendor that sells retro game products at 1.5-2x the usual asking price (they sell for more than what you might find on ebay for instance)
The biggest gripe I have seen is people being upset that they sell supposedly refurbished game consoles that have dust inside of them, scuffs and generally aren't worth the asking price (with no way of knowing what the actual condition of the console will be in before it arrives)
People also dislike them for supposedly causing some inflation in the prices of retro games
The way I see it tho, it's really your own fault if you are going to pay those ridiculous prices when you can find the product for a much better price on ebay
It's like getting mad that a thrift store sells old pants for $20 when you could just go to goodwill instead