I don't do consignments, but the contracts I have seen the split is based on the selling price. Also, the FFL and the customer should agree with the asking price, as well as the process of any reductions in the price. If the FFL puts it on the shelf at a price higher than the customer agrees to, then it could take longer to sell, which may not be in the best interest of the customer.
The bottom line is that the contract should detail all of the issues.
FFL Transfer/Special Order Dealer since 1993.
Net-FFL list maintainer.
Never try to teach a pig to sing. You waste your time and you annoy the pig. - Robert A. Heinlein