Maybe. If you calim to wash a million cars but only wash a thousand that will be obvious, but 10 washes different is lost in the noise. Nail salons are easier because you can have the expensive personalized service that no real person buys but if someone investigates you will give it to them.

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.