Any inspection gives prominence to the vehicle and confidence to the seller provided it's done by somewhere seen as reputable, which does obviously include the dealership network.
Check your local automobile club, by which I mean the types of organisation that provide breakdown cover and recovery services such as the RAC, AAA, etc... These typically have an accredited inspection service delivered through their network which will carry the kind of providence that a buyer would be looking for. As an example, in the UK the RAC offer such a service - details here
The risk you run using a local mechanic, unless they are part of a recognised service network the likes of Bosch or Halfords in the UK, is that a buyer will be suspicious because they may think you have a personal relationship with the mechanic.