I'll be in Athens in late January with a biz colleague. We'd like to find a good private tour guide. Any suggestions?
I'd suggest checking the RS Greece or Pocket Athens Guidebooks, as there will be good, reliable Guides listed there (I didn't check). If you can't find the books at your local Library, check larger Bookstores and just make a note of the information.
You could also do a search on Trip Advisor and look for the highest rated Guides there.
Check with Fantasy Travel and Dolphin-Hellas Travel, both in Athens, to see what they might have to suggest. Both have websites. Who you hire will partly be determined by the sort of tour you're envisioning, and these travel agencies are skilled in helping with that, so provide details when you make inquiries.