There's no reason they can't be uninstalled carefully and reused.

But..... it requires people taking their time and being careful which doens't seem to be a hallmark of the subs you are seeing.

I would agree to reuse but have strict requirements for what damage from removal that will be acceptable - get agreement and hold people to their promises. Ask for a finish guy / punch list person to be the one to remove - those folks are more careful as they are used to working in peoples' HOMES and not a jobsite.

Remove them yourself. That way you'll be certain they aren't damaged.

He has to remove them anyway. Make your condition inspection after they're removed. It's not a difficult process. Film it with your phone if you want to create a record.

I advise letting the contractor remove and reinstall the vanity. After the work is completed, address any issues that exist at that time. Hopefully (and probably), there will not be any issues to address.

If you can be "made whole" by having the vanity, mirror etc. reinstalled in a manner that the end result is as if they were new and newly installed, it should be acceptable. Set parameters with the builder to what is acceptable for the reinstalled item's appearance and performance.

I would not recommend removing the items yourself unless you want to learn first hand how difficult it is and open yourself up for potential blame.

@Mark Bischak, Architect: "I sit in my master bathroom and see how perfect the tile work done by the professional is." Gazing at the tile work... a gas chamber would limit your view. No wonder you hate those ;)