holding back funds that belong to me *******ly

Once again bid or buy are with holding funds that belong to me in my account their excuse is that if you sell a lot and make a good amount of money they want to check to see how you made it .... this is ***** on their part as all the funds were paid thru bid or buy by either eft or bob bucks so all this money is now in their account and they dont want to let it go ... I have been selling on bid or buy for years now and feel this is a poor show of very unproffessional behaviour on their part - can anyone assist as it doesnt say anything in their rules and regulations that they have the right to hold back someones money????