Make sure they used (the right) sealant on the tank access panels. The clew, when they're full, is if fuel oozes out.

It's not uncomon for the seal not to be complete. Even Hincley's vaunted service team made that mistake on one of my tanks when they polished them 3 years ago. I had a sending unit that wasn't working, it turned-out to be a ground. Then a couple of years later, when I had my tanks cleaned (because I didn't use the fuel in the inflatable tanks), one of the tanks had a little "moisture" from fuel along a portion of the "seal" when I "overfilled" the tank. I had the top resealed and it's been good.