You would need to accept the coins, deposit them into a Wasabi CoinJoin and if Wasabi declines them, send them back and keep the bike..

Sounds like a lot of fun! Honestly, I don't see people switching from fiat to Bitcoin if that's the intended (by Wasabi team) way to accept Bitcoin..
Well it's not something so strange, and I see no difference with what's happening every day.
People return stuff purchased for cash all the time for bunch of reasons, paypal cashbacks, people don't like bike, people changed their minds, card declined,
tainted stolen cash bills, fake cash bills...
Maybe guy who pays don't even know he is using stolen marked dollars, so he needs to accept return and pay with real dollars.
Fake cash bills? Yes. That's why in cash trades, I want to see the bills coming out of the machine or quickly put them into an ATM myself while the trading party is on the spot.
But tainted / stolen? Hell no. The ATM will suck those in, no matter if the buyer of your bike stole them from his roommate or even from a large robbery.
What's worse: in 'Bitcoin taint', you could even be deducted some of your balance way down the line; imagine this: the crime just happened, nobody even knows about it. Your bank accepts the cash. Months later, your bank account is suddenly in the red, as your funds are determined to derive from fiat that has been used in a crime
before you got it [you're not the criminal], so it's frozen forever.
It's not how it works in fiat, but it's how it works in Bitcoin and that's why it's such a big issue.