i have a few phrases that could not possibly be considered negative comments but sort of damn with faint praise fortunately I very rarely need to use them mostly I just do not leave feedback for bad buyers and block them
example
" once completed this transaction was just about OK"
and for anyone who claims item went missing in the post
" sorry item did not arrive, refund has already been processed" which if it genuinely went missing will be the only one if they keep getting similar feedback it acts as a warning if I think they are genuine I may mention something like "polite patient buyer" ie they asked me politely when it was sent, how long should I wait and it was resolved without case being opened