the only concern would be if the tank had air in it. they can put a little propane in it and vent. the propane is heavier. (real world, the velocity will mix it for a few minutes). (after they make the hose to tank connection, they should let a little propane go thru the connection to atmosphere before they tighten their hose to the tank just to get any air out from the connection area).
there is a relief on the tank if there is a pressure problem. on one that has been filled before and hasn't been left open, very low chance of anything but propane being in there.
when u start using it, if there is any air, it will be the first thing out.
shouldn't be any concerns abt any gas using appliances.