You're not allowed to require it, but you can cancel orders for any reason, and thus always come up with "another" reason why someone who won't FE should be canceled. There's no good solution to this. There could be a lower tier vendor status for $150 where the vendors must take orders and can't force FE. That way if you're not a scammer and you have a legitimate product to sell you can do it for a lower price. However, those vendors would be victims of reverse scammers. They could "buy protection" with the $500 tier, but then we're back to where we started, so might as well just have one tier.