Can glottal stop occur if there is consonant before a T like in ' Best man"
... but not best man. I've looked through the Wikipedia articles on Glottal stop - Wikipedia, Glottalization - Wikipedia and No audible release - Wikipedia and can't find any mention of the st combination.Yes; some speakers will use a glottal stop rather than a /t/ in some words, such as bolted, wanted.
It's just the simplification of a consonant cluster. I don't think it is even possible to say a glottal stop after /s/ unless a vowel comes after the /t/.I don't think so, but you might hear the 't' being sort of omitted (I suspect there is a technical word for it) and sounding like 'bess man.'