marketer vs marketeer

_dkg_ asked me:

this fairly irrelevant language question just popped into my head, and yer the only person i could think of who might have an interesting (and possibly valid!) take on it. here's the question, put vaguely:

what's the difference between using an 'er' suffix as opposed to an 'eer' suffix?

( more related musings )

For a non-linguist, these are some pretty sophisticated questions, which reassures me that one doesn't have to have a post-graduate degree in order to ask useful and interesting linguistics questions. As a first stab of answering them, let's consult the Oxford English Dictionary:

( fair-use quotes from OED )

You may note that according to the OED, the -er and -eer suffixes are descended (at least for some of the -er examples) both from the OF -ier, as you might have guessed, except that a few of the -eer examples are indeed from Dutch. I've highlighted in strong those bits that _dkg_ spotted on his own. Well done, sir.

And yet, there are a few questions still left open (are there any phonotactic rules for the use of -eer, for example). Any takers?