That's why popular businesses for money laundering are car washes and nail salons. They're mostly cash based, and have very little in the way of inventory, so it's easy inflate your sales.
Especially if you stick with quarters instead of using game cards like most modern arcades. Since quarters would be recycled anyways (Taken from the games and restocked into the quarter machine), it makes it easy to just deposit the cash you want to launder as if it had been fed into the quarter machine.
More likly the above are selling something illegal though. Pay for the expensive hand car wash but get drugs instead with a cheap automatic wash - nobody will know the difference.
For higher valued goods they use horses. A saddle can go for $30,000, so you buy some $1000 saddles and sell them for $30,000 and $29,000 worth of something else.