They weren't making 7.62x51 NATO ammunition when Mercury dimes
were being made -- the dimes ended production about 10 years before the cartridges came into existence. ;)
Seller uses a guaranteed money-making tactic, that's not illegal, although perhaps slightly unethical.
Step 1 - buy a bunch of old coin rolls. These are easily available and extremely cheap, all the way back to the 50s.
Step 2a - find a coin series with high collector interest but which also has common dates available in BU such as Morgan dollars
Step 2b - alternatively, simply stick any old coins into the old rolls
Step 3 - every few rolls (maybe every 5-10 to every 100 or more depending), insert a semi-key date or key date coin into the roll, or a couple of coins from other series in the same denomination, so that buyers have a "treasure find" story to provide testimonial. Alternatively, stick two BU common date coins on the heads and tails end of the roll, and fill the middle with problem coins, culls, average circulated common dates, etc.
This method is surprisingly easy and has no shortage of suckers willing to toss large sums of money in your direction, guaranteed.
Looking at one example from this seller, a roll of Walkers with two shiny end coins is selling (currently) for $328. You can buy bulk average circ. to VF Walkers for $7, and AU/UNC for $30, so assume the roll is 2 BU end coins and 18 ave. circ. middle coins, giving you a total cost of, say, $180: ($7 x 18) + ($30 x 2). If it sells for $400, you just made $120. On a single roll. And he has hundreds listed. Even if you splurge on nice XF/AU coins as the middle fillers, you can still clear over $50 per roll on average without any trouble at all.
A so-called "Uncirculated" roll of Morgan dollars
with "CC" end coins sold for $2,800. Figure the roll is two MS63 1883-CC's at $170 each and the middle is 1886, 1887, 1884-O, etc. in low MS for $30 each. Seller in that case would have a cost of $840, and make almost $2k in profit.