I joined a couple of networking groups when I was in insurance and the local chamber of commerce and still keep in touch with some of the members.
The networking groups are not free that I joined.
There is also toastmasters which teaches people to do public speaking and mastermind groups.
And there is always volunteer opportunities to socialize as well.
I would be leary of joining a mystery shopping group with a bunch of people I do not know--that is just me, though.
Most of the people I still keep in touch with from these groups do not know I mystery shop. I just go to the seminars to learn about stuff and socialize.
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Two wrongs don't make a right, but three lefts do.