Another thing to (re)consider is the entire 'trust' issue itself.
I consider it it bit like this. If I don't trust a developer enough to provide them with sufficient access to the 'live store' (so they can complete the 'whatever'), I probably wouldn't trust them enough to perform the 'whatever' in the 1st place.
Conversely, as a developer, if the client doesn't have enough trust in me to provide the level of access I need to complete the task asked of me, I really don't want anything to do with the task in the 1st place. Its just trouble waiting to happen. This situation will never end well.
It is a two way street. The trust has to go both ways.
It is unrealistic to expect clients to have the knowledge and know how in regards to setting up special FTP accounts, etc for developers use, even if it is good and recommended practice. Likewise, it is also unrealistic to expect these clients to spot any nefarious code introduced during development, and although the idea of doing all development 'off site' and having the client upload the final product to their own site seems simple, even this is a bit much for many (for various different reasons).
I'm not in any way suggesting that merchants shouldn't takes steps to prevent their trust from being abused by an unscrupulous developer, but what I am trying to suggest is that not all developers are unscrupulous. They'll be in the minority, I'm sure (the main thing being is that we only ever hear the 'horror' stories, which gives a biased perception).
In my opinion, the biggest concern about hiring a developer isn't so much a trust issue, but more of a competency issue. Unless examples of previous work can be demonstrated, this is a hard call to make.
Just a little more food for thought.
Cheers
Rod