My personal opinions, and I don't decide scammer tags:
I'll get the easy ones out of the way.
3. Should people be stripped of any special titles - especially titles like "VIP member" which imply credibility even though they are bought - while their obligations to their users are unmet?
Yes, should also be removed before scammer tag is applied if there is sufficient cause to do so. Pirate for example (he didn't have one) during the grace period he was given.
4. Should we disallow the promotion of other services by people who have already failed to meet their obligations in respect of one service?
No, everybody makes mistakes, screwing up once doesn't mean they shouldn't be allowed to try again. Many entrepreneurs declare bankruptcy at least once in their life before becoming successful. Besides that's what the scammer tag is for, to warn people. If they don't have a scammer tag for whatever reason, that's what the community is there for.
5. Should we ban people to whom the scammer tag has been applied?
Not as a blanket rule, no. There's no reason to remove their ability to express themselves just because they're a scammer. Besides, banning them would remove any incentive for them to repay and ensure they just return under another account (not that they don't anyway).
1. At what point should a "scammer" tag be applied to people who owe members of this community money and who are clearly making no effort to ensure the money owed is paid?
I'm not a big fan of policies that dictate
x results in scammer tag because that would result in people abusing the system and intentionally falling just short of
x in order to avoid the repercussions. Also saying
x will not result in a scammer tag will end up with people doing that intentionally. It's also not fair to say that when there may be special circumstances that would make a scammer tag inappropriate.
I also don't like answering hypothetical scenarios, because there's a lot of information, words, context, extenuating circumstances, etc. that aren't given. Just results in a bunch of arguing over semantics. Very few things in life are black or white.
I think reneging on an agreement is about as clear as it gets, and adding in a bunch of clauses will result in more harm than good.
2. Should we have a separate tag which advises people to be cautious in dealing with people who owe money but who don't yet meet the benchmarks for applying the scammer tag?
I don't think it's needed, the community is quite capable of doing that themselves.