If you want to sell a SBR'd lower, the buyer fills out a form 4 and writes DOJ a check for $200. Once the transfer is approved, it becomes cash and carry. Another option would be to mail ATF a letter indicating that you're returning the gun to Title 1 status, whereby they'll remove it from the registry like GTG said.
It is not like selling something here on the classifieds, it is actually a lot better because the people that own registered firearms tend to not be ****ing idiots.
You're not helping the case of going SBR with these comments Having to fill out a form 4, and add $200 to the cost of doing business, then have to wait until the transfer is approved... you'd have to really want the SBR. I'm not of that mindset, so I'm not all that keen to go that route. As for selling here and having unpleasant experiences, I'm guessing you were unfortunate enough to run into such a prospective buyer. I haven't, so it's not been an issue for me.
To the OP, my apologies for derailing your thread!