I attended USC and so am somewhat familiar with Charleston, and have completed a few historic walking tours as well as a horse/buggy tour. I discovered Oyster Point from a Southern Living city guide, and WE LOVED IT!! First, it's a reasonable $20/per person. They offer 3 times throughout the day and booking online is breeze. My husband and I booked a Monday at 11:30am and were paired with one other couple.
Palmer was our tour guide and she was awesome!! She kept it interesting, asking us questions and quizzing us on a few points of note, offering to take photos of us along the route, etc. The pace was easy, steady and she even builds in a bathroom stop. Palmer was extremely knowledgeable about the beautiful city and clearly enjoys her job. We brought some extra cash for a tip, too. We would recommend this tour and even do it again the next time we are in town! :) Thank you!
(NOTE: speaking from experience, the horse/buggy tours are hot and cramped, and you cannot pick your own route--save yourself and take this easy-paced walking tour by Oyster Point!)