Yes. They take a cut of everything all the time. Depending on what you're doing, you might be better off firing them, then re-hiring them. Note you LOSE the initial payment! You need to decide if the percentage loss is greater than the re-buy.
e.g.
If they take 10% and their re-buy is 100k, if you're only going to do 50k of trade before using them again, keep them.
If you're going to do more than 2 M in trade, fire them, do the trade, then buy them back - you lose less overall, because 2 buys is 200k, but if you kept them they would take at least 200k, if not more.
You need to consider the balance carefully.
I suspect it might be better to just keep them, especially if you do combat often.
