"Simple really" is the answer. You send me a low resolution mono mp3 of your stuff, I put it into my DAW, then I record my guitar part, I mix it down to a low resolution mono mp3 and send it back to you.If you don't like it, you owe me nothing! If you do like it, you pay me via paypal and then I will put the full quality (44.1khz 24 bit usually, but it's up to you) file on my server for you to log into and download. I normally put a totally unprocessed file up for you so you can do whatever you want with it, but I'll also put up anything else I came up with. I cut the files exactly to the bar lines so you can import it straight into your DAW with the minimum of fuss. As you can see we don't even need to be on the same continent! It's all done over the net.

Usually I discuss with the client exactly what kind of feel they are after, either over the phone or Skype before I do any recording. No fiddling with midi controllers... or pesky pitch shifting/time stretching, you get a great guitar take that fits your track perfectly.