Dealing on Ebay is an both an art and a science. This particular seller has not sold anything for months, and suddenly appears with several pieces of Theta equipment.
When in doubt, follow this rule for Ebay: Sell all you want, but never purchase.
Alternatively, if it is a purchase which is significant, the seller should have no problem permitting this to be an i-escrowed transaction. If the seller refuses, one can only conclude that he does not want the buyer to have the opportunity to inspect the goods before approving payment.
Would you buy from a store like that?