I do frequently refer people to other sellers if I really think it will help them, and I tell them I can state what I know because I know the seller or have used them myself, but can’t guarantee what their experience will be. I don’t give them links because Fiverr seems to flag for almost any link in an inbox message, on or off Fiverr. I just give them the username in most cases. So far no one has ever come back to me to say that something went wrong. I have had some come back to me and complain that the other person is too expensive, but I don’t really worry about that.
Fiverr hasn’t ever flagged me or asked me not to do referrals as long as I don’t give a link. If the buyer seems exceptionally difficult, I do spell it out and tell them to put in the fiverr URL followed by a / and then eoinfinnegan, but that’s special for the ones that I really find problematic.