Personal cleaniness and hygiene is also an issue.
On the first occasion a very smelly and obviously homeless person got on and sat next to me, at a table of 4, with another man opposite. Fortunately the homeless person got off again at the next stop, the smell was quite offensive, but about about five minutes later a small dark brown/red 'thing' was crawling on the table, I popped it with my fingernail against the table, it was definitely a flea. The man opposite me looked at me and said, 'Was that what I think it was?'. I texted my wife, and she was waiting at the front door with a black bin liner, my clothes went on a hot wash and I went in the shower.
The second occasion we were doing a supplier evaluation in Liverpool, I had travelled to Liverpool South Parkway and met my colleague there. The factory was a rat infested hovel on the banks of the Mersey, with a complete absence of health and safety. I was all for making our excuses and leaving but my colleague who was a commercial person said 'no we have to complete it', the work they were tendering for was part of a government contract. I always carry overalls, a good job too, the place was filthy, not helped with unprotected shot blasting taking place in the main shed that served as a production area. When we came out I was filthy, I looked like I had been down a coal mine. When I got on the train to come home I got some odd looks, but washing up at the site was a no go, think 'Trainspotting' style toilet, cold tap and no sink. So I had to travel as I was. Once on the train I went to the disabled toilet and cleaned up a bit, at least my hands, forearms and face were clean, but that just drew attention to the rest of me. On the last bit of the journey home one of the guards, who I saw fairly often said "where the hell have you been" and I told the story. Needless to say the company we visited never got a sniff of the business.