Just what would said contract look like? Did you have an attorney draft a contract and then give it to the seller? The seller would then have to have his attorney review the contract before agreeing to sign it. That's a whole lot of hassle for simply selling old equipment I no longer wish to keep.
If I were selling something and you wanted to go that route I'd decline to sell to you. However, if you had already sent payment before I had sent the merchandise, I'd simply return the payment to you.
I sold a 5.1 satellite system that was new in the box (AV123 whatever it was). The buyer sent me a check and it turned out he was an attorney because his letter with the check had letterhead with his firm's name on it. He didn't require any silly contract and with me it wouldn't be necessary anyway. I sent the speakers and even had to follow up with UPS because they got the address wrong the first time around. But that's how I work - he sent me the check in good faith and I made sure he got what he paid for.
The contract was a 'simple word' contract. No more than what was being sold and the terms. Terms stipulated that if the seller failed to send after payment confirmed, jurisdiction happened in my state. If the terms were I would get the item first and then have to pay and not do so, then jurisdiction would be in his state/county. Terms were I send payment, then he sent product. It all worked out.
It wasn't a problem since the seller had no intention of backing out.
Check out a book called "How to Get Your Money and Still Keep Your Customers". I picked this up for $5 and it has literally enabled my business to collect over $20K though the courts with businesses that thought it was ok to get our solution and then give us the bird on paying for it.