Putting aside common sense, which is the norm on some of these threads, a yid walking into a new shul typically doesn’t first search for a seating chart hidden behind the door or wait for the gabbai sheini or shlishi (who was supposed to be standing by the entry door and instead is schmoozing with his chevrah by the bimah) to point him to a seat not covered by the local minhagim governing makom kavua. My experience is that 9 of 10 times, you walk in and absent a simcha where you search out the family, you take whatever seat appears empty.
Edited -79