well i have seen many a buyers calling sellers idiots here openly in the forum or on feedbacks. other words used are fraud, worst seller etc.
i would only submit that no one has any right to use derogatory language against anyone. i am sure 99.9% people will never dare to say so face to face. the anonymity of identity should not be used to belittle others. as the founding principle of ebay says " we believe all people are basically good people"
especially if you can see the seller has been consistently been able to meet the commitments, if he has failed to do so in ur case, it must be out of some extraordinary circumstances, since there is nothing to gain for him from troubling u in any way, more so since he doesnt even know u personally...
its a humble request, one should avoid such words. it can demoralise a person who is putting sincere efforts but at time may face situations where he is not able to meet the commitments
warm regds