Couple other things to think about. When you make an offer to purchase, you will have a due diligence period. That is the time where you will have access to the house to have home inspections, survey, appraisal, ect. If something comes up in the appraisal or home inspection that will change $$ figures, you can renegotiate the price or ask the buyer to pay to have things fixed.
Couple different kinds of money also. You have due diligence money and earnest money. Usually the seller will ask for one or both.
The earnest money is paid directly to the seller for them to "take the house off the market" while you are working on getting your loan finalized, inspections, appraisal, etc. This is kind of a good faith payment that comes off the sales price showing that you are serious about buying the house. $100k sale price - $2k earnest money = loan for $98k. The seller can cash that check and do whatever with it. You will not get this money back if you walk away.
Due diligence money is a check that you write to the real estate company. Another kind of good faith deposit. The real estate company holds that money in escrow until closing. If you walk away from the purchase during the due diligence period, you get the money back. If you go thru with the purchase, that amount is deducted from the sale price. $100k sale price - $2k earnest money = loan for $98k.