1. Not researching coin values beforehand can lead to missing out on valuable coins.
2. Overlooking small change or foreign coins thinking they are not valuable can be a mistake.
3. Ignoring damaged coins may cause you to overlook rare coins with numismatic value.
4. Not bringing a magnifying glass or loupe to inspect coins closely can result in missing important details.
5. Failing to negotiate prices can lead to overspending on coins that are not worth the asking price.
6. Rushing through a sale without carefully examining each coin can result in missing hidden treasures.