One is a list of forbidden words (or character combinations). That's what tripped you up. One of the brands of sneakers/trainers that spammers often promote is Hermes, so we'd blocked that term. I've taken it off the forbidden list. The spammers have been less active recently, so we'll see if they start using it again.
The other strategy is IP blocking, but we only invoke that for repeat offenders.
There is a character limit on messages, but we have that set obscenely high. There's also a time limit between posts from the same IP, but I forget where we have that set.
We're always sorry when someone gets inadvertently banned, but we either have to take that chance or make folks set up user accounts. Shoot me an email if it happens again.