My experience:
I've used Fiverr to get professional drum tracks, and I am very happy with the outcome.
1. Seek through the drummers and read carefully in terms of styles they play well/mostly and what their influences are.
Also pay attention to what their kit and recording setup are. You want textures and tones that match your own material.
2. Specify your recording format (24/48 or 24/44 for instance) and make sure tracks are delivered in that same format.
3. Create a song, create a Wav click track for the tune. Use Wav files for high-quality remote work.
Stories from people using Mp3s for collaborations have been that after repeated openings/closings of the files, the way Mp3 truncates its files can lead to subtle sync issues when re-combining the tracks for mix. Stick with Wavs for max. quality to work with.
4. Add as much in the way of instrumental scratch guide tracks for the song as you can, to ensure the drummer hears at least some dynamic moments where he may put emphasis.
5. Be very descriptive of the style of song, what you are after, and what some drum examples may be from other songs. The more the drummer knows, the more he can accomodate your wishes. Your arrangement/song structure is what he is playing to, so have it in your head or on tracks before ordering.
Usually with Fiverr, people offer tiers, with my drummer offering a couple of recording packages with fewer/more revisions and such.
Decide what you need, but if you come to the end and need one more "go" at one part, just negotiate something for an extra fee.
Best of Luck,
C.