The easy way is to check the marketplace as suggested
The hard way: you need to find an address like a coworking site that can verify for you this by receiving your postal code
You could also get someone to verify for you, a local verifier. I've seen business that made fake photos and placed them like a local curator and then prepared "the site" to be verified for local rep/verifiers at random.
I think you are going to invest more the hard way, both in time and money at the same time.
Consider that the marketplace sellers could have either an unexplained method, a contact among local reps or a real site where they receive the postal cards, making this easy for you.