Recently I found Foobykamikaze — a user with trader grade A+ but when I checked his profile before starting trade I saw that his last activity was 2 years ago so it’s useless to trade with him!!! And quite often I see users with grade A- which are inactive for a half of year or more.
My thoughts and understanding of the trader grade:
The trader grade is a ratio of expired trades to the total amount. So you can evaluate chance that your trade will be accepted or declined but not expired.
But it doesn’t count user activity. So we can have users that are inactive for months or years but have a low percentage of expired trades (and hence high trader grade). However, since they don’t respond to the trades their percentage of expired trades grows (and trader grade decreases) but looks like this process is slow and sometimes is too slow.