I think it depends a lot on what types of domains they are.
If you have a big, popular, tourism related geo in a .com .org or .net you will likely get a great sale through a Sedo or Flippa. If it is a smaller city or region you may want to consider making calls to that the local region.
If it is a pure geo like cityname.com or townname.com there are a number of passionate locals who will be interested in it. Just have your target price in mind and get ready for a lot of haggling.
If it is a geo like lawyerscity.com or automotivecarecity.com things get a little more tricky. These are usually more difficult to sell and are highly dependent on the size of the city or region, the income, population, etc. A lot of these types get unloaded here or on eBay for what is hardly a reg fee.Occasionally though you find one that goes for a lot more because it is one of the more desirable regions.
Without anymore information it is really hard to give suggestions.