They send very unimpressive people to buy your device. Once with you, they start to negotiate. Their standard tactic is for you to accept lower price for your device by putting the condition of your device as average, even if it’s in good condition. After all a used device will always have some signs of usage. In my case they declared a small scratch on my iPhone 7, just 7 month old device, as a dent. When I told them that dent means body is pressed and deformed, while scratch means paint is affected. I had declared cracked glass and scratches on my phone body. Their aim is to beat the price down to a level lower than what you can get in exchange offers in the market.