First of all, I'm sorry that this happened to you...it really sucks..
Based on the guy's feedback rating (I didn't read the actual feedback), I'd speculate that he didn't get the cabinet new and just passed along what he probably bought cheap from someone who took the speakers out... At least I'd give him the benefit of the doubt and see what happens.
Looking at the auction, I'd guess by looking at them that the speakers weren't EVs...perhaps this is because I knew that they weren't before looking, but to me, they don't look like EVs (the frame edges are too thin and the domes are too large). EVMs have a particular visual presence that my eye picks up on... But, I'm old and anal and have been studying these things for years...
I'd like to offer some unsolicited suggestions on where to go with this...
1. Looking at the B52 link that was posted, the cast frame speaker below the ones you have look like a cast frame Eminence...perhaps the stamped steel frame speakers you have are Eminence too. Is there a small silver label either on the side of the magnet or stuck to the inside of the frame that has a larger number starting with 15 followed by some numbers and a smaller sized number starting with 67-then four numbers? If so, it's an Eminence and you can get the Thiele-Small parameters for it by writing to
[email protected] and giving then the Spec No. (the one that starts with 15). That will help you/us determine if the speakers are a good enough match for the enclosure.
2. If the seller is cool about the whole thing, ask for a partial refund of the $400+ that you spent on the cabinet. Assuming that he didn't purposely swap out the speakers himself, he may have bought the cabinet as-is and shouldn't have to give it away...the Mesa cabinet itself has significant value (both to you and future owners).
3. I know that you wanted an EV loaded Mesa cabinet, paid for one and that's what you should have. But how does it sound with the properly wired B52s? Would you be happy with it for now if you got it for a lot less than $400? Try to keep an open mind on this one...it may sound pretty good how it is and there might be a price that you and the seller can agree on that may help you both put this behind you...
How ever you approach it, be sure to be calm, polite and stick to the facts. As one who has received gear that is substantially less than described and one who has sold equipment that was damaged in transit, I've learned that the resolution goes much easier if the tone is kept polite, respectful, factual etc (as long as the other party is responding in kind of course...).