There's a lot of factors at play here wed need to see the coins to some extent to see what's going on. If they are all polished MS coins, to put a shine on them, then as was said carrying one around in your pocket for a bit will take the shine off and turn it into an AU and not a problem coin anymore however it won't get MS prices, and it won't get a "MS details cleaned" grade.
Really depends on a coin by coin basis. The value, the condition, and if in fact it has been cleaned or the dealer is trying to get your coins at a steal.
If someone shined up a XF coin trying to make it look MS that can be problematic. What it comes down to is the rarity and condition of the coins to determine the best course of action. Sometimes it's better just to leave it as "MS details cleaned" of there's a dramatic difference in value due to rarity between AU and MS.
As I said determining the best course of action should be done on a case by case basis and while knowledgeable, dealers aren't always right, nobody is always right, it was his opinion and it always benefits a dealer to talk down a sellers coins so they can pay less. Not saying they all do it, just saying it can happen.
So how about we start with an example picture of one of the coins in question and see what everyone says here?