Appraisals are a normal part of the home buying process when financing is used. Even when someone is paying cash for a property they have every right to have an appraisal done. Whether or not they can object/cancel based on an appraisal depends on how an offer is written.

When you are buying a home that is a new construction, also called a new build, it too will require an appraisal by your lender. Building a home can take anywhere from 3 months to longer than a year. If it's less than 3 months I would be a little bit concerned about quality control. Typically a closing will take 30-45 days on a normal sale, and as a result there can be some confusion and an appraisal can be ordered when someone is buying a new construction.

This isn't always a problem, because the appraiser can get their hands on the contract and any change orders to give them a good idea of what the finished product is. The problem comes in when they do the appraisal before all of the change orders are done. This can happen for several reasons, usually because the buyer wants to change and/or upgrade something after the appraisal has been done. It can happen because materials used aren't always in the paperwork the appraiser has.

Avoiding this problem is done by communication with the lender, the builder, the buyer, and the appraiser. Essentially, no matter how you want it to happen it will not unless the Realtor is involved. Even if something is missed, it should be in the appraisers hands with plenty of time before closing to update the appraisal. The lender should be the first one to catch a problem because the appraisal will come back for less than the contract price. It can be addressed, but only with plenty of communication... otherwise it's going to cost the buyer time and money to make the sale happen.