The addendum will list the changes to the original agreement and the date of the counter offer. All parties must sign off on this addendum. You may accept the buyer's offer but with contingencies. But be wary of accepting contingencies that will result in realizing less profits from the sale of your home than you intended. To expedite negotiations, offer to split the difference if you are close in price.
Buyer refuses to provide pre-qualification letter.
It is reasonable to request the buyer to obtain the necessary financing before you take your house off the market. Determine if there is an issue with financing, or any contingencies that might delay closing, before you make the final call. Buyer's mortgage terms unacceptable. You should not enter into a contract when terms are unacceptable, especially when the contract is contingent upon the buyer obtaining a specific interest rate or points. Buyer has little or no money for deposit.