No, because I'm talking about intentions and motivations, not actions. I said it's reason to believe that someone has intentions/motivations to have an affair; I didn't say it's enough to believe that someone has had an affair.

The reputation, marketing, and design of guns is a good bit more varied than Ashley Madison's. But yes, buying and learning to use a gun shows a certain intention or willingness to kill. It may be to kill a deer you're hunting or to kill a person in self defence, but in general it's evidence of a certain willingness to kill.

You're making a lot of false assumptions. You could be the owner of gun, intending to fire it against inanimate objects only. Like a paper target at the gun range.

One could even have bought it out of simple curiosity.

Yes. And you could be a member of Ashley Madison who's just curious, or who's doing a documentary for Al Jazeera, or who's trying to see if your spouse is on it.

I was speaking generally. I said that it's reason/evidence in favour of a conclusion. I said that it isn't proof of it. Those kinds of general rules and presumptions are useful for all kinds of things and in all kinds of ways. Or do you think that our judgements should be entirely composed of perfectly comprehensive and universal rules?