Buyer with FHA loan requires a second "Appraisal Contingency"

[Kay March]

A potential buyer of a single family house has presented an offer based upon an FHA loan, which, of course, will involve a pretty stringent appraisal. Nevertheless, he has attached an "Appraisal Contingency" which allows him to hire another appraiser and present the appraisal to me, the seller, up to 7 days prior to closing. If the appraisal comes in low, he can walk away at that point. So he appears to be giving himself two chances to present me with a low appraisal. Would any seller who is not desperate to sell accept that? Am I missing something?