Often buyers do not have much of a chance to look at or think about their purchase. Houses sell quickly and often get multiple offers.
Homebuyers who bid high on a house that just came on the market may not have taken the time to really think it through. They develop a severe case of buyer’s remorse and want to stop the purchase.
Usually, the house can be put right back on the market and if there were multiple offers the seller can accept another buyer’s offer. Home sellers can and should keep collecting offers until the sale closes.
There really isn’t any way that home sellers can prevent a buyer from backing out. Even buyers who offer a lot of earnest money will back out early enough so that they do not lose their earnest money.
Sometimes home buyers will ask for a lot of repairs as a way to back out of a purchase. I had some buyers that did that a few years back. Instead of telling me that another home was on the market that they liked better they came up with a lengthy list of repairs and upgrades.
When the sellers said no they canceled the purchase, got their earnest money back and immediately made an offer on another home.