At this moment you can only trade a Mk1 (white) quality modules/weapons. My suggestion is to allow players to trade modules of all qualities (Mk1-Mk5). To balance this - those qualities can have a different minimal prices - i.e. the white Mk1 module would cost min 60GS, green 80GS, blue 100GS, purple 120 GS and orange 150 GS. In my opinion that solution would boost trading volumes significantly, will help players struggling with credit income and allow a class of crafter/trader players to emerge.
Similar, allow selling of multple stuff through the ‘trade’ menu (when you right-click a player)? If you want to sell 30 monos to someone you can add max 3, so you need to send 10 emails (or do 10 trades)