Assignment fees PLUS mark-up?

[Austin Lowe]

I'm beginning my first wholesale deal, and I'm confused about the assignment fee. I have the seller, and we've agreed upon a price of $250k. I believe that the property is worth $270k ($20k mark-up), which is what I would be asking for from the buyer. 

Now, regarding the assignment fee: is this amount in addition to my mark-up of $20k? For instance, if I ask for $270k, and my assignment fee is $5k, would that make my profit $25k ($275k total)? Or would the buyer need to know the agreed upon price between me and the seller, therefore, my assignment fee would be $20k, bringing total to $270k? Also, is an assignment fee required? Or can I just mark-up the property? 

I haven't been able to find a clear answer on this, and any help would be greatly appreciated.