Reading the original post, it seems your VERY sensitive to how you're treated, and that's probably a big part of the issue. Sounds like you walk in a little "raw", very aware of the treatment you "deserve", very aware of every word said in greeting, every real or perceived lack of attentiveness.
Any checks are a red flag, big checks are a blazing red flag. Now that debit cards have been invented, two types of folks write checks:
1. Honest people who are eccentric and won't use a debit card. And oh, they have their "reasons" and I'm sure we'll get to read them in this thread, but they are really eccentricities.
2. Other folks with less wholesome motives.
Unfortunately, the only way to know if you are in the first category or the second is to call in the check.