Should I sue this buyer?

[Kay March]

Selling a SFH. Buyer's agent told me today that the buyer can't proceed because of a low appraisal on her own home, which killed a sale. The buyer's agent is talking about an appraisal so low that it's completely unbelievable, and he won't respond when I ask to see the appraisal. I'm thinking of suing the buyer for her deposit. Has anyone else been in this situation?