Help with selling GAS preamps

Hi, I just discovered this site while researching the preamps my father gave me to try and sell online.
I have been having trouble posting them on Ebay. Perhaps someone here can help me? Should i make listings here and is that better? I did not see any listings for any GAS company electronics.
I have 1 Ampzilla 2 Son of ampzilla and a Theadra
Any info on these systems would be great help thanks!