Richard,
Sometimes, syrup in the can crystallizes, usually when stored in too cool a place for too long a tome. Then the stuff that pours tastes like dishwater. The fix is putting the can in simmering water and shaking or stirring it to get the crystals back into solution. Was that your problem? I once bought a gallon of maple dishwater and returned. The grocer tasted some and was aghast. His bulk stock had crystallized, and I got the liquid over the top. He returned my money and found several more cans like what I had bought, but one (old stock) that was fine, and he gave it to me but wouldn't let me pay. I helped him empty all of the watery cans back into the drum, which he expected to redissolve. That's tricky, though, with a 55-gallon drum.
There is plenty of good maple syrup on the market. I know nothing of FDA standards, but if it wasn't crystallized, you probably got ripped off. There are industry standards, and most producers adhere to them. I've collected sap to fill the vat on the sled and worked shirtless in the steam house, so I can give you the straight dope.
Syrup is made from the sap run in the spring, In the morning, the fire is started while the first sled is loaded, with the pan off to the side. When the fire is hot and the sled arrives (better a horse or mule to pull it, but a few strapping lads can manage) the pan goes over the fire and the sap -- it's like water -- goes in. Pretty soon, it boils and when it's thick enough -- 11 lbs/gal is the standard, by law in VT, NY, and elsewhere -- it's ladled or drawn off into cans or sometimes drums but some remains in the pan and mixes with the fresh sap of the next batch. The first (and maybe the second) batch has a light flavor: that's "Fancy"; I generally avoid buying it. The next is a bit darker (more of the original batch has caramelized) and is "Grade A". That designation applied to several batches. It has more flavor and is what I use for gifts. After a while, the stuff is real dark and the flavor a bit too strong for my taste. Some producers reduce it to 13 lb/gal and let it cool in molds, where it crystallizes. In pieces, it's maple candy; ground up, it's maple sugar. Usually, it's sold as Grade B. I buy Grade B when I can get it and mix it 50:50 with cane syrup of the same density. That moderates the strength of flavor (and lightens the very dark color), but the flavor of the extra time under heat comes through and I like it.
All this time it's so warm and humid inside despite one end of the shed being open that water collects on the walls and floor, and a shirt is a discomfort. (But an outside temperature of 20F is considered warm.) Every once in a while, someone takes a ladleful of hot syrup outside and decorates the snow. The stuff soon solidifies, and you eat it like a lollipop with built-in handle. The kiddies usually traipse over for their share.
By this time, the fire is usually allowed to die down, and the pan filled with snow and scrubbed down. (so that tomorrow starts with Fancy again). If there are a few sleds of sap still outside, sometimes the work continues by lantern light, and the result is "Grade C". I've heard it said that "C" is for "Commercial", and though I doubt the origin, it certainly is used that way. Straight, Grade C is a bit bitter and too strong to be enjoyed, but when you see a pancake syrup with "with real maple flavor" on the front label and "3% maple syrup" on the ingredient list, bank on it being Grade C. With grade B, you just wouldn't taste 3% at all.
Jerry
P.S. Sometimes, the same equipment is used in the fall to turn cider into apple syrup. That's another wonderful flavor.