in a way, he may be telling you the truth. maybe he doesn't have a good serving tool and isn't very good at it. if you want a good center serving that won't slip, it helps if the string is under more tension than the bow will put it under. if you serve tight enough for it not to slip while its on the bow, many times your peep will rotate a good bit when it didn't before. this is because the string got all twisted up while re-serving. you can work around this and have it come out pretty darn good, but not everyone is very good at it. i do think you can get good at it though. there is a serving tool called the beiter winder. its pricey, but compared to the others out there - its a rolls royce in a world of geo's. since he's a tech or even owner of a shop - he should be able to do it well - but maybe every time he does it, it just comes apart. i really had a hard time with it staying together for thousands upon thousands of shots until i was able to wrap a tag end under almost the entire run of center serving.