I burned out two phones using them as hotspots, a colleague did the same to his. All there were motorola phones on verizon, with a sealed in battery (moto razr).
in weak reception areas, the phone would overheat, even just using the phone itself to surf, hotspot and multiple computers exacerbated the problem.
I've seen that in my new Moto X (2015) as well, it gets very warm when doing a lot of LTE traffic in marginal signal areas. Although hotspot is unlocked on this phone, I'm hesitant to use it excessively as such, as the battery is again sealed in (didn't learn my lesson last time)
Contrary to what others are saying, it's my opinion the sales person was being honest with you, it is not BS.
