Hi there, wouldn't say it is customary, but sometimes the seller requests it of their agent or it becomes a customary practice of the particular listing agent. By the time of the walk through, negotiations are done, and and so while more times than not, the listing agent does not accompany when I am representing the buyer, I don't see much of a downside if she/he is present. If an issue does surface, all parties are focused on resolution and so if all hands are on deck - it could facillitate resolution of any issues. What would be uncomfortable would be for the sellers to be present - I've only run into that once, and it was my seller, they just needed the peace of mind - and insisted on being there to have it - before getting into their packed vehicle and driving away.
Good luck to you,
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