I thankfully found this site when i began considering chins and looking into getting one. I even adopted my little guy off this site. My biggest oops was raisins. I read quite a few "reputable" looking sites that said it was ok. and even encouraged using them to bond in the beginning (Shoots ranch for one did, and they looked big enough to know). I'm glad I only did TINY pieces and I figured-heck, he likes other treats too, and no one debates if those other ones are bad, so quit using the maybe bad treats. It's not like Yuki can cheat on any diet I give him.
I also just generally wasn't prepared for Henry's personality. Reading about how chins can be sensitive, shy creatures and should be left alone quietly to settle in a new home left me expecting him to be a delicate exotic flower, and did nothing to warn me about the demented exotic squirrel-thing who, the first day I brought him home, demanded attention and refused to settle till I let him out to look around the room. Apparently he didn't read the bit in the chinchilla book that said he was meant to be shy. (he probably just ate it)
I also wasn't as good of a chin proofer. I had no idea chins could pick up and throw cardboard pieces. So I had to figure out a better way to keep him from eating/chewing on a plastic baby-gate.
I was really lucky I found this site. I got an amazing chin, all his actually good chin-safe stuff, and a ton of good knowledge. I never had the "oh crap I just bought a bunch of junk" to deal with.