Sorry for cross-posting this message, Im new in this field...
A friend of mine submits the following question:

Being a descendant of Salomon Levy LEYDESDORF, born in Presburg
(Bratislava) in approx. 1750, he became a citizen of Sneek in The
Netherlands in 1796. At the same time, a Salomon Levy Leydesdorf -
also born in Presburg - lived in Groningen, which is also located
in the northern regions of The Netherlands. One of the two must
have been a impostor, maybe even both.

How did people prove their identity in the 18th century when they
moved to other countries...?

Thank you beforehand for your reactions.

Evert van Engelenhoven