[Shutter]

This isn't a bad idea, and since it would be voluntary, then if its not your style, its not a problem. The fact is, you can't run entirely off trader ratings. If a person has never bought or sold before, it doesn't make them a scammer, although anything is possible. I wouldn't have been able to purchase my AEG, or sell the couple items that I have if people ignored those who aren't involved in large amounts of transactions.

Which isn't to say don't read trader ratings. If a person has negative or even neutral transactions, take that into consideration! It means they've had less than stellar dealings in the past, don't expect yours to be different.