Do you still use Flippa to sell domains?

No. Flippa stopped to be "attractive" years ago, unless you wanted to pick up a decent name for few bucks.

No, not anymore after they increased their listing fee I'm not using.

no, it always fail to verify whois, too troublesome to add domains there

Nope haven't used them since it was changed to $25 to list a domain. Still monitoring their platform though to see what type of quality domains sell there.