Never base husbandry decisions on what you see done in pet stores. ....Ever. All they care about (99% of the time) is saving money while selling as many animals as quickly as possible...which always equals poor husbandry choices.

I understand how easy it is to assume your snake and gecko WANT a companion...but honestly, that is just us projecting human (or at the very least, social mammilian) feelings onto a creature that is completely alien to such things. Female cresties can get along fine in an enclosure if its the right size and set up properly for them...but that doesn't mean they NEED to have a "companion." So long as they have a clean, comfortable, secure environment...and enough of the right kind of food...and fresh water....they're already as happy as reptiles can be.