Even in the 80s there were only 4 reasons to run a cash-only business.
1) You don't want to/can't afford to pay the credit card processing fees, or pay employees to process the checks.
2) Too few of your customers have credit cards or checking accounts.
3) You don't want a paper trail, to maintain your customers' anonymity.
4) You want to skim revenue to minimize your tax burden.
No 1) fails to meet the smell test because at $150+/hr each individual transaction would be totally worth the cost to process it.
No 2) fails to meet the smell test because your clientele for a $150+/hr tennis club are rich people -- who universally had such things in the 80s.
No 3) fails to meet the smell test -- assuming this was a real tennis club and not a "tennis club" whatever bizarre thing that euphemism would have meant -- because using an expensive athletic club was seen as a status symbol, not something to hide from the world.
No 4) is not only highly likely because of the absence of other plausible explanations, but also because we know Trump is a grifter, cheat, liar, crook, etc. It's entirely consistent with our prior knowledge of his character, behavior, and business practices.
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