Well, let's say I wanted to buy other's gig for real and left a review and he/she did the same and bought my service what makes us getting banned for this ? I need their service and they needs mine I guess it won't harm.
Its not a problem for once but if you use it aggressively then you may face a ban . If you do anything, do it well or you may not see good consequences later on. I would be interested in your offer but will you be the one sending first order or me ? If you have any other account on fiverr like that of friend's one then it would be a good idea to use that account rather than the one on whom I am supposed to post a review .