Gold cards

I just use them to make 50 players without checking their price cuz im lazy and impatient but some are worth decent coins

Exchange up to the 50 cards and sell those or build the sets and sell that.

Selling them individually will always be the best way...if you don't wanna do that then you can put them in sets for the 50 and then sell those cards. If you really wanna speed it up...QS them for training and then buy cards with the training.