I've seen junk, but no arguments, on Antiques Roadshow
I've been watching Antiques Roadshow for ... um ... decades. (I'm not addicted! I can stop at any time! Usually between seasons.) They do show items that are not valuable for various reasons, such as the item is a fake or (as you surmised) because the item is a reprint/reproduction/was mass produced. Sometimes because the market has dropped. ("X years ago, this was worth Y amount, now it's only worth Z dollars.)
I've also seen it go the other way, where somebody thought the item would be worth a few hundred dollars and find out that it's worth much, much more. There have been several people who looked so shocked that I hoped that there were paramedics standing by.
I have yet to see anybody get mad at, or argue with, the appraisers for a bad evaluation.