Well, it is interesting. I have played several people who serve illegally. You know, things like throwing the ball at the racket instead of tossing it. I have also had people who serve like that tell me that I am serving illegally. It is funny. If it is someone who does not know the rules it is a different circumstance than someone who does know the rules. I would not let it get you mad. Often, people who tell you that your serves are illegal are using game strategy to try and get you mad. If it gets you out of your game that you have been told your serves are illegal, that is not good, even if you are enough better than the person to beat them easily.
One thing I would do is have a coach, at some point, look at your serves and see if they are legal. Many people do serve illegally without realizing it. I was playing with some friends about a month ago. And I was watching one guy serve in a match. Now this guy is much better than I am and I was not playing. I was just watching. And I noticed that he was not actually tossing the ball more than 2 or 3 inches. I told him that it did not matter to me, but that, none of his tosses were high enough to be legal and that, he probably should change that because at some point, someone is going to make a big deal about it and that person will technically be right even though, this guy was not getting any advantage from having a toss that was not high enough. Almost every pro does something that is borderline or straight up against the rules. But, it is worth having someone who know the rules watch you serving and see if there is anything that is borderline, or against the rules.
Then you can explain the rules to that person and show how your serves are actually by the book. Or you can ask the person what he thinks you are doing that are against the rules and have him show you as was suggested above.
It usually does not matter to me if someone serves illegally, so in a match I usually would not say anything myself. But it is worth checking and having someone who really would know, see what you are doing.