I go to a lot of antique auctions locally and at those the buyer and seller each pay a 10% seller's commission or buyer's premium for a total of 20% to the auction house. I'm just curious - would those who think a 15% fee for the seller is too high be OK with 7.5% each to the buyer and seller? That would seem to soften the blow for sellers and still allow Moniker to net the same.
Whether the "buyer" pays the commission or the "seller" pays the commission or it's split some way is meaningless, assuming folks are rational.
e.g. if a seller pays the commission, and the item sells for $1000, the broker middleman gets $150. The net proceeds to the seller is $850.
If an auction has a "buyer's premium" of 15%, the rational buyers will take into account the commission, and bid $1000/1.15 = $869.56. The commission with then be 15% of $869.56, $130.44, and the total paid by the buyer is $1000, as before. The seller gets $869.56 instead of $850, because a discount of 15% is different than a premium of 15%, as the bases will be different (but they're roughly the same).
A similar thing will happen if the commissions are split in some manner.
Only non-rational buyers and sellers would be fooled by such games (and non-rational buyers don't last long in business). It's very similar to the situation where goods are sometimes displayed with sales taxes already in the prices, vs. priced normally, but then taxes added at the cash register. It's really no difference.