Every once in a while, someone will post a question like this and then get angry and refuse to believe us when we tell them the truth. Glad you are willing to listen. I'm not saying every comment is always correct, but you get honest opinions.
If you want to look at examples of various error notes, check out the back of the Standard Catalog or other banknote reference and you will start to get a better idea of how each type of error presents itself. You can also look at certified examples at HA.com for more references. For instance, ink errors (ink smears, solvent smears, insufficient inking, etc) tend to look a certain way or appear in a typical pattern on most bills. This may also help you avoid the fake error salespeople on eBay and elsewhere.