I've always had on-site appraisals where the appraiser did need to see the inside of the house.
An appraisal without visiting the property does sound like a scam, how do they know the inside of the house is not gutted?
I can understand why the bank requires an appraisal, so it's not purely a scam, but I don't think it's an accident that most appraisals come in exactly at the selling price. The bank needs some independent 3rd party to verify that the house really exists and is not completely trashed. I assume the appraisers usually just take the selling price and work backwards to find comps and adjustments to support it rather than starting with the comps to come up with a fair selling price.
Though that's not always the case, I did have an appraiser save me $20K once -- the appraisal came in at $25K under the accepted offer price, the seller asked me to kick in an extra $25K on the loan, I said I couldn't. They asked me to meet them half way, and I said I couldn't, but I'd offer an extra $5K. They accepted and the deal went through.
The seller appealed the appraisal (the comps weren't perfectly comparable), but they already had a property lined up to purchase and didn't want me to walk, so they finally accepted the lower price. A month later an identical property in my complex sold for $50K higher than my original offered price (so $70K higher than what I paid). The SF Bay Area is a weird market.