I'm not totally against it and I have been known to take the odd sniff of the inside of their shoes, once I start taking their shoes off, but I don't think I've ever done it to their socks. By that stage though, I'm already getting on with the tickling, so no time with sniffing socks.
Have tickled feet and they got sweaty and what ever lotion they applied to there feet you can then smell which was nice and did make it better never sniffed directly but have tickled smelly feet also but and it wasn’t as good but I wouldn’t say i go out my way to sniff them no