Is it normal to buy used shoes?

Yeah, I think that's totally fine, good idea. You probably save some money, and help curb environmental impact too.

I've saw girls sell their old worn out/trashed high heels on some auction sites think some guys have a fetish for worn shoes

Good idea. Thrift stores are the way to go. Save money, the style can look pretty classy if pulled off the right way. My father and I pick up old gas station items from people in the hills and back woods to restore amd resell. It is actually bringing in quite a good profit and we meet and see some great things that I can't believe have survived all these years sitting outside or in an old shed.

I don't agree with buying used clothing unless you have no other option. I see this because of leftover body sweat, lingering body odours and dead skin, etc. It grosses me out.

I prefer vintage shoes; they feel more comfy. Most of my shoes are old.

Is it possible to get some disease from wearing used shoes? If not, sounds like a pretty smart idea!