Is it permissible to complain about food prepared by a halal vendor, knowing that the Prophet (peace be upon him) "never criticized any food whatsoever"?

It is disliked to disparage food offered for free, based on the hadith: "The Prophet (peace be upon him) never criticized any food ever." Doing so breaks the heart of its maker and reciprocates kindness with ill-treatment. However, if the food is a commodity for sale, the buyer may object to its quality if it violates agreed-upon or customary conditions. This falls under demanding one's legitimate rights and is not a sign of ingratitude for blessings. Nevertheless, one should be gentle with the maker and speak kindly when advising them.