Well, my previous own camera was a Canon 7D, I was the third user. It was externally worn out, previous owner really fielded it. Worked like a charm for thousands of photos. Its still in good working condition, simply I don't use it anymore.
You always buy new, but still someone will buy your used camera. The X-T3 I bought was in perfect external condition, I gained trust in the user who was a professional photographer, having this one as backup. I ran some test before hand and I am pretty sure it was not defect when I got it. So I don't blame the seller. Perhaps the one you sold will unfortunately go wrong in 6 months, or in 10 years, who knows ? As for me, buying it new would have save the repair cost if the warranty was still running. Somehow, I lost my bet this time but it's fine, I'll get a X-T3 with a brand new upper part. Simply I did not save that much money due to the repair cost.
I am a bit more shaken in my choice of entering Fuji system. I found out that the issue I faced was not unique, and several users reported it. I saw in another post (the one I erroneously posted in first) that people had the feeling of a quality drop between the X-T3 and the X-T4, this leave me a bit dubious as I was already not seduced by the X-T3 external build quality.
This has nothing to do with the picture qualities, which are perfect for me. If the defect does not come back, then I am good. Fingers crossed.