I wasn't meaning to sound overly critical, but first gecko or not, a degree of research is always required before purchasing any animal. A google search for "enigma leopard gecko" reveals two videos, in the 7th and 8th spots respectfully (both on the front page) that clearly display enigma disorder.
I honestly don't think the gecko acted badly with the seller. I could be wrong, but as one who has bred many enigmas, I've had enigmas that acted perfectly fine one day and then went completely bonkers the next for no apparently reason. Every enigma displays at least some sort of movement disorder. It comes with the trait.
Both the buyer and seller are at equal fault in my opinion. The seller for assuming the buyer knew of the enigma disorder, and the buyer for not doing simple research ahead of time. Although I personally would have provided a refund both in the best interests of the gecko and for the satisfaction of the customer, an enigma with a head tilt can still be a very healthy gecko and thus wouldn't void any health guarantee.
Anyways, I feel like I'm repeating myself unnecessarily and clogging up the BOI, so unless more information reveals itself I will not be posting. I feel genuinely sorry that the buyer had a negative experience with his/her first gecko purchase, but the experience was somewhat self-inflicted.