First time BRRRR In Need of help - Question about auction

[Jimmy Jacob]

Going through my first BRRRR and am scheduled to close on my first property this week. I'm purchasing a house on assignment from a wholesaler who won the property at auction for X plus a 10% buyer's premium, and then paid the auction company a deposit. I agreed to buy from the wholesaler for Y.

The closing documents have me reimbursing the guy his deposit he originally paid the auction company. It also has me paying the 10% buyer's premium to the auction house. All of that is in addition to the purchase price of Y. 

Is this normal? The assignment contract does not address the deposit he paid or the buyer's premium I'm now expected to pay. Only the purchase price with my own deposit due to the title company when I signed the assignment contract.