Do wolves keep their proficiency level when traded?

And therefore is training up wolves then selling them a profitable model?

yep! they certainly do

the only way they lose it is when they’re not being used for that role, or in hunting, that position

Ah, so they will lose proficiency while sat in the trade centre, it doesn't 'freeze' them?

So (if I do this) better to advertise through the forum?

probably, but they do tend to sell pretty quickly depending on their stats & how you price them