He could have made it fit, but obviously doesn't know some of the tricks other plumbers use. Terry has discussed this a couple of times in the last week in posts here.
Basically, consider that the outlet from the toilet is about 2-1/8" in diameter, and you must have at least a 3" pipe. So, you can fudge the location of the toilet a bit with the slop in the bolt holes in the toilet. If that isn't enough, you can opt to install a repair ring over the existing flange with the bolt holes closer to the 12" a normal toilet would use and bolt the toilet to that. It gets a little trickier to seal the repair ring to the old flange, but doable.
FWIW, most of the Toto toilets that use the UniFit adapter (most of the skirted toilets, but not the Aquia) have a nominal 3/4" behind them to the wall on a perfect 12" rough-in, so most any of those would fit.
It really isn't all that hard to install a toilet, had you considered doing it yourself?