- Fix a security bug/TODO by having seller send back the signatures rather than a full blown transaction (which would allow a malicious seller to try and confuse the buyer by sending back a completely different TX to the one he proposed)
- Introduce an UntrustworthyData<T> wrapper as an (inefficient) form of taint tracking, to make it harder to forget that data has come from an untrustworthy source and may be malicious.
- Split the giant {Buyer, Seller}.call() methods into a set of smaller methods that make it easier to unit test various kinds of failure/skip bits in tests that aren't needed.
