It's a likely scam, you're right to suspect it. Most likely they're not interested in the name, but instead are part of the appraisal website (whose name is infringing on ICANN to lend credibility, and created this November), and are trying to get you to purchase that appraisal only. You buy, it's far lower, they back out.
I'd respond with something like "Since you're willing to make an offer of $10K, I accept, and we can arrange a deal though an escrow site for the sale. No need for an appraisal, since you already made an offer I feel is fair for this domain.".
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