From what I understand, they dont try to build syrup from scratch, it's more that they cut the real thing with sugar and water. According to wikipedia, maple syrup is basically 2/3rds sugar and 1/3rd water, with about 1% "other".
If you added the right proportion of sugar and water to real stuff in a 50:50 ratio, I'd have a really hard time distinguishing that from the natural variation in taste strength.
Luckily I have a steady supply from people I trust. I can't get enough of the stuff made over a wood fire.