An appraisal isn't an exact science
When appraisers evaluate a home's value, they're giving their best opinion based on how the home's features stack up against those of similar homes recently sold nearby. One appraiser may factor in a recent sale, but another may consider that sale too long ago or the home too different, or too far away to be a fair comparison. The result can be differences in the values two separate appraisers set for your home.
An appraisal is a snapshot
Home prices shift, and appraised values will shift with those market changes. Your home may be appraised at $150,000 today, but in two months when you refinance or list it for sale, the appraised value could be lower or higher depending on how your market has performed
You can ask for a second opinion
If your home appraisal comes back at a value you believe is too low, you can request that a second appraisal be performed by a different appraiser. You, or potential buyers, if they've requested the appraisal, will have to pay for the second appraisal. But it may be worth it to keep the sale from collapsing from a faulty appraisal. On the other hand, the appraisal may be accurate, and it may be a sign that you need to adjust your pricing or the size of the loan you're refinancing.