Sometimes it's, besides SEO, which is connected to it, a pure marketing. Say you are a serious seller and want to sell some of your 500 common coins among 500 scarcer and some rare. You will price 100 of your common and scarcer coins at good prices to attract a customers who miss 5-10 of them. A customer, for the convenience of a bigger order will also take another 15 common coins, some of which are a little bit and some are much more expensive than elsewhere, say 20 euros instead of 5 for a common coin. You can price a rare coin high and somebody could catch to it, as many collectors nowadays don't have patience for waiting for a coin to show up somewhere for several years.
There are these other, "stupid", small time sellers who just put up even higher, ridiculous prices for some coins in case someone is crazy enough and they're in no need for the quick money. Doesn't need to be laundering necessarily. My holiday home neighbor sells his house at 2M euro although the market price is at most 900K. He doesn't really want to sell it, but if somebody's willing to pay that amount, well...
I see the problem of reselling own coins at big auction houses. One Austrian house is often selling coins from previous auctions as a part of their strategy no matter it was bid on by the real people. Guess it's a kind of reserve price, but they attract bidders with low starts. Although that kind of rigging the market prices should be illegal, as it's not only irritating, rather fraudulent, I guess nobody cares since they pay the difference tax on fees from the hammer price.
Rigging the own bids is yet another subject...
