Issues with purchase. Seller is being very fickle

[Mike A.]

I've been negotiating a contract for a 20 unit building. Funding has been secured and a letter as well as proof of funds has been forwarded to the seller. On my 1.5m offer, I stated I'd put down 50k and 1031 the rest; which was verbally accepted. The seller is now requesting 10% down. One, that wasn't in my offer. Two, the seller has been very fickle with the sale of the building. We've actually been negotiating since February and I've already walked away once. I also do not trust the seller as he will not certify the profit and loss statement. He will only sign the statement saying with the best of his knowledge, but is providing tax returns for the last three years on the property.

Any suggestions on what to do here?