Dumb guys in pet stores are quite a common thing. Sure, there are good ones but it is not the norm.
The gel in the bottom of the plants.... It is likely a moisture reservoir of some sort. Sort of like the stuff in disposable diapers. It absorbs 100 times its weight in water and holds it unless sucked out by capillary action (ie roots or tiny mouth parts). Though the plants could also be hydroponic and the stuff could be some sort of medium. Either way, I would remove it and rinse the roots in water before adding the plants to the tank. I like to eliminate the posibility of adding anything to my tanks.