I bought underwear and shorts from several guys on ebay. I would often compliment on how hot they look in the pics they posted and how nice the underwear and shorts were. Then if the vibe was right, I would be bold enough and ask if they had the same pair that was used and unwashed OR if they could customize the pair they were selling for me (wear at the gym/during workouts and runs, wear it for a couple of days and to sleep too, jack off while wearing it and shoot some loads in it; treat it like a cum rag). It often works out pretty well.
The best incident was a marine I met selling a pair of running shorts on ebay; he always wore them as underwear. I happen to have the same pair of running shorts and also wore them as underwear. After a couple of email exchanges through compliments and some flirting - we ended up agreeing to swap our identical running shorts with our similar customization request (as mentioned earlier: wear at the gym/during workouts and runs, wear it for a couple of days and to sleep too, jack off while wearing it and shoot some loads in it; treat it like a cum rag).
That was my best swap ever; he smelled awesome!!! Loved how it turned out; smelled super ripe with a ton of sweaty stains and cum shots that made it crispy (I later sprayed a little water in it to make it slimy again). I went to the moon and back sniffing his running shorts while I was jacking off and had one of the best orgasms from it. I also put in on and jacked off in it too, shooting my loads in them, mixing our cum and scent together, and feeling his smell over my body.