Im having issues with my fuel gauge occasionally going out and the dealer that I had it replaced by 3 times said that the next time it happens he's going to blame it on the head unit. I thought he was full of it until I talked to one of the guys who installed it and he confirmed that it can mess with my gauges

So 1. Are they both full of it to get more money out of me or 2. If this is true is there a way to fix it?