Asexual, unmarried and with traditional scruples about sex, simply not in a relationship at present and not inclined toward casual sex, in a strictly monogamous relationship with a partner who is currently travelling ... there are really quite a lot of possibilities.

I agree it's more likely that Lumifer does have sex sometimes, and no doubt there is some give and take involved. However, this need have nothing to do with what any normal person calls "buying sex". (There is an argument to be made that, e.g., in some cases marriage can be viewed as buying sex, and no doubt there are other things in relationships that can usefully be thought of that way. But that's far from what would have to be true to justify claiming, in the absence of any actual information, that Lumifer buys sex.

I don't agree that Lumifer was failing to engage with the point of the previous comment. I think the previous comment was in fact where the rot set in. Lumifer expressed a particular opinion about how buying and selling should work. (As you might guess if you happen to read the whole discussion, I am not very sympathetic towards this opinion, but that's irrelevant here.) pjeby then threw out a needlessly inflammatory and logically incorrect generalization, to which Lumifer replied with the contempt it deserved.

(Needlessly inflammatory and logically incorrect because: 1. the position Lumifer was espousing was specifically one about commerce, and there is no reason to assume that the same principles govern commerce as personal relationships; 2. Lumifer was not in fact defending lying, and one might reasonably think differently about lying versus letting someone believe something incorrect; 3. bringing sex into any discussion is liable to elevate the emotional temperature, doubly so when you start making accusations about the other party's sex life.)

The particular remark Lumifer made was pointing at objection 1: the distinction between commercial and personal interactions. The fact (assuming it to be one; I haven't checked that Lumifer wasn't lying and it's none of my business) that Lumifer's sexual interactions with other people aren't commercial is entirely to the point and not at all a "random thought-stopper".

And no, the give-and-take in typical romantic/sexual relationships is not of such a character as to make them just like typical commercial buyer/seller relationships, which is why it was in no way appropriate in this context for you to claim that Lumifer does buy sex.