Beware of an individual or group of people who call themselves Investment Bankers or a Buying Group. When they cannot provide you with personal financial statements or a financial statement from their company, you have a very slim chance of ever closing the transaction. The seller should have a copy of the financial statement from the buyer attached to all offers.
If your most qualified prospect submits a Letter Of Intent that includes a lower price and more generous terms than you had wanted or a less qualified buyer has submitted a more attractive LOI, then now is the time to negotiate with the stronger prospect. It's almost impossible to improve the deal once you have accepted (by signing) the Letter Of Intent. However, the buyer may find reasons to re_negotiate a lower price during the due diligence phase.