Purchasers can just make up numbers for repair requests?

I accepted a lower offer on my house, given a $3,000 waiver on repair costs as to the best of my knowledge from a previous inspection anything needing fixing would more or less fall under that number. Inspection happens, buyer demands $7,000, graciously dropping it to $4,000 as agreed. I have a contractor go through with the inspection and price fixing the things listed as defects: $3270. Where did the extra four grand come from? It is a mystery. Under the contract if there is not an agreement over repairs within seven days the buyer just up and walks after wasting my time, so far as I can see there's nothing stopping them demanding a million billion dollars and no requirement that their request bear any relationship to reality, leading me to suspect that their $3,000 waiver was a con from the get-go and they always meant to demand far in excess of that amount at this stage. Am I with no repercussion?