In many cases, a mortgage appraisal of your home when selling it will be necessary for your buyer to obtain a mortgage. Lately this has become a problem because appraisers look at history to determine value rather than what the market may be doing today. So, in a hot market, your home may sell for more than the appraised value. If the home does not appraise, your buyer may have to come up with more down payment to qualify for the loan.
Even so, you want your home to appraise for top dollar. So get rid of clutter so the appraiser can see the home. Spruce things up. Paint exterior wood work if needed. Do some work on the landscaping if over grown. Plant some flowers. The appraiser is just like anybody else. Some of what they do is predicated on emotion; but most of what they do is based on recent comparable sales.
When negotiating your sale, the real estate agent must put in language to deal with the eventuality that your home may not appraise for the price agreed to in order to prevent the buyer from coming back to demand that you lower your price. Of course, in a hot market, there could very well be cash buyers and or other buyers that can come up with the down payment to close on your sale. Don't waste time with buyers that don't have money to close your sale.
Your real estate agent will demand proof of funds to close the deal and should require the buyer to show that they have money beyond the initial down payment in the deal to close the sale. You can even make the deal not contingent on mortgage qualification. This is a seller's market in many areas so the seller gets to set the terms of the deal if the buyer wants the home.