The current Tip section can come off rude to buyers. Seriously, "Show your appreciation to XX by leaving a tip"? Didn't a buyer show their appreciation by paying for the agreed amount they asked for? In my case, I required less than what the service detailed and paid more than what was originally asked. The current Tip section can make a buyer feel like buying a service is not enough.
This section needs to be optional and the message should say, "Would you like to leave XX a tip?" or Would you like to leave a tip?" with the action options below being
"20%, 40%, 50%, Custom",
"Tip Now" "No Tip".
(I graphic designed and attached an example "fiverr_tip_suggestion.jpg")
This way the buyer doesn't feel like it's gratuity instead of tip. Especially, if the service was bad.