How is an appraisal different from a price check?
In short: A price check is a number. An appraisal is a number with a purpose, a definition of value, a date, a method and a signature, so someone else can rely on it and check how it was reached.
If you only want to know roughly what a card sells for today, a price check is fine, and you can do one yourself in a few minutes. It is not something you can hand to anyone.
An appraisal answers a narrower question ("what is this worth, for this purpose, as of this date?") and shows its working. That is what an insurer, an executor or a court asks for, and it is why I do not give quick numbers in messages. See will you tell me what my card is worth in a message?.