My understanding from what I have read from the oasis team is that almost no one uses multisig. Not only that but people are going further and releasing funds before receiving their product.
You're right. FE is common practice. Sellers hate multi-sig because of a) bitcoin volatility and b) because they want the bitcoin in hand. And buyers will do whatever the biggest trusted sellers want and buyers accept that every so often, sellers will exit scam. Seems like it's a seller's market. If sellers start demanding XMR, then the buyers will acquire it. If not, then not.