So you've managed to avoid all the previously mentioned mistakes and the negotiation is going smoothly: this will result in a win-win situation for all involved. However, you're beginning to realize how much you've invested in this business and feel you cannot afford to part with it, so before closing the deal you decide to back out at the last moment. We call this "seller's remorse".
If there is ever any shred of doubt prior to beginning the selling process it's important to address it. If that doubt still persists, you are not ready to sell your business. Simply do not begin the process all together and spare yourself and your family the headache.