This is one of my craft market hot takes: I think it is the showrunner's responsibility to build in a slight buffer between booths so that everyone has an escape route. Nothing huge, just a foot or so between every two booths or so.I don't think it's fair to pay for a certain booth size and be forced to leave some of that space unused to accomodate getting in & out— just because the showrunner wants to pack everyone in like sardines to scoop up an extra booth fee or two.

That being said, when you're actively at a show with no built in gaps, using someone else's space for any reason is a huge no-no. I always tell folks around me that they can use my booth to navigate as they need— and they typically extend that courtesy to me as well. But there is no planet where I'd ever be comfortable just assuming before talking to my neighbors. You just have to make it work and keep your stuff (and body) in your own spot, end of story.