We had such a visit recently; we were so appalled at the very idea that DwB would stoop so low as to send door-to-door solicitors around the town, that we immediately assumed this person was scoping the block for a potential break-in. Because he asked about our neighbor and we accidentally let it slip that he's away, we put up a hidden surveillance camera[0] overlooking the stairway and both our doors' for a couple days, just in case someone decides to come back at night. We also immediately queried Doctors Without Borders about this, warning them about a potential crime done using their brand.
Imagine our surprise where Doctors Without Borders responded to confirm that the person who visited us was, in fact, legitimately soliciting donations for them, and that they actually do door-to-door. Something in me died that day.
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[0] - We repurposed a nanny cam for this, where by "nanny cam" I mean Ubiquiti G4 Instant, because the only way you can get a baby camera these days that doesn't send videos of your kids to random third-party servers is by buying industrial surveillance hardware.