Eh, not really. Most half-decent businesses have a privacy policy/TOS that explicitly makes this a no-go, and would be grounds for a lawsuit if a company posted a customer's conversations with said company. It doesn't look like Historious has such a policy, so legally it might be okay, but it's still scummy IMO.
Posting your side of the story is fine, but using communications that are expected to be private usually isn't, and you should be able to correct the story without posting private info (we don't even know if the transcript that Stavros posted is true.. he could have completely made it up for all we know).
With all that said, it made me curious to look at the TOS for IMGZ, and... yikes... https://imgz.org/help/terms/
I mean c'mon - have a little fun.
At any rate it's classic absurdist marketing, and I approve.
Besides, I don't read the TOS of most other services. Why would I start now?
Just think, if this were a larger company doing this, they would be absolutely crucified for deceiving customers by hiding critical info in tiny text or TOSes that nobody reads.
And FWIW, I haven't actually tried paying yet, but if IMGZ is handling any actual payments info, a clever TOS that says "we don't make any promises about your privacy" won't protect you from fun legal action if that info is ever breached (though I'd guess and really hope that Stavros is using some payments provider like Stripe or Paypal).
Just think, they said wistfully, how angry we could be if things weren’t such as they are. What a glorious, outraged life we could be leading.