When I was a grad student, I used to sell mushrooms at a farmers market. I simply enquired about renting a table and that was that.
The thing is, fresh mushrooms can be difficult to supply consistently. For example, morel season is short-lived and a dry mid-summer will cut your supply of other mushrooms.
So I dried my mushrooms and packaged them. I bought food-quality bags and made nice professional labels. I collected, processed, and packaged the mushrooms and had 5 good weekends of selling.
It was a blast but realistically it was not an efficient use of my time, from a monetary perspective. I did it mostly for fun and because I was studying mycology, but I don't think I'd want to calculate the cost in time/gas/materials vs. what I made. There is always the potential for liability too; not necessarily poisoning someone, but if someone has an allergic reaction or is nervous about eating wild mushrooms they could make a big stink.
I sold dried Boletus edulis, various bolete/Suillus spp., Hericium, Hydnum, morels, Marasmius oreades, lobster mushroom, wood ear, chanterelles, and, when available,fresh mushrooms like Pleurotus, blewit, Armillaria, giant puffball, and Lactarius deliciosus. I also had some dried mushrooms used for dying, and sample dyed wool yarn, like Phaeolus schweinitzii, turkey and false turkey tail.
