Well personally I haven't bought mushrooms off the street in over 10 years so I don't really know what is out there. I see your point though. They can just throw whatever the hell they want in those bags. Although, I think if people were out there throwing toxic mushrooms into bags and selling them as shrooms it would be a huge news story. The media always likes to grab ahold of negative drug stories and run with them. Not saying it hasn't happened, just that I don't remember seeing any news stories about it.
Do they bruise blue? There are several species of panaeolus known to grow wild in Florida, so it isn't out of the realm of possibility. All I know for sure is that the mushrooms in those photos are not psilocybe cubensis. Proceed with caution.