I bought a 4' vanity base from a Craigslist ad. It was perfect to replace
the "builder grade" crap in the master bedroom and at a really good price.
There was a problem, though. When I got it home I discovered it was exactly
48" wide, the exact same width of the area in which it was to reside.

The vanity to replace (since torn out) was at the end of an 8' corridor,
with a walk-in closet on the left and the door to the bath on the right.
Each of these doors had 3/4" trim, narrowing the maneuvering space to
46-1/2" inches.

Needless to say, something 48" wide would not pass through a 46-1/2"
opening!

Plan #1.

Inasmuch as the door trim was not removable without gutting the door, I
elected to disassemble the new vanity and reassemble the parts on the other
side of the constriction.

I now have a pile of miscellaneous pieces - some broken - that will not go
back together for love or money. (One has to press-fit the sides on to
various horizontal slots cut on the side pieces. There is no way to perform
the pressing, since I can't get to the sides.)

The face of the vanity still looks super, however.

Plan #2 (Pending)

I'll rebuild the freaking "box" out of a generous stack of 1/2" plywood I
have in the workshop just waiting for a project. Then I'll attach the front
and all should be well.

Maybe. There's still the distinct possibility that I'm cursed.

MORAL:
"Measure twice then, er, do something or other."