I know this sounds silly, but I tend to just trust people - a legacy of living in Japan I think, where I've never met a dishonest person. Incredible, I know, but true. That's not to say there are no dishonest people in Japan; of course there are but it was something I never gave a second thought to. I could give countless examples of their honesty.
In my days as a butterfly in Thailand I had many total strangers come back to my room. Valuables were kept in the safe, but nothing outside the safe was ever stolen. Perhaps I was just lucky.
The only incidence of theft I've come across in Thailand was when a boy in a massage place in Pattaya stole my very expensive watch after I'd left it behind. I went straight back to get it but in those few minutes it had magically disappeared.
We have to be responsible for our possessions and in that case, I wasn't. I only realised once I was on the plane that I was still wearing it. Normally I bring a cheaper watch which, if stolen or lost, would not bother me.
Also, it was my fault for leaving it behind.
Overall, I find the Thai boys very honest.