Idea: ignore offers we already know are invalid

[johny-b]

1. I receive an offer
2. It happens to be invalid, I get an exception as in #2199
3. I'd like to never again see this offer (and never again get the same exception)

What happens now is that (I'm not 100% sure though) I start negotiations from this offer in every run and they fail every time.

[mateuszsrebrny]

Placing in backlog, will discuss when planning Q4