But a car wash uses water and a nail salon hires workers. Shouldn't take long to check that those numbers don't add up with what was sold at the end of a month.
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.