The custom-made computers powered by pepperoni pizza

Just ask them to send you an invoice. I was in a similar bind decades ago. There was Western Union, but too much hassle. "Can you send me bill? Here's my name, address...that way you have a paper trail". At that time, mailing invoices was common. They did, my company paid them too. If I recall, it was for $0.99.

I'm more intrigued as to what the machines were, and why Windows NT wouldn't run properly on them.

Same

From the article:

“ “Will you take a corporate check which I promise to put in the mail?”

She was sure this wouldn’t work.

“You will?!” ”

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What if a check was never sent?

Eat the cost and never accept payment by promised check over the phone ever again.