AS couple of quick thoughts. Most mechanics charge more if they install parts you bought. This is to make up for them not being able to make money by marking parts up. And also, make sure your mechanic has dealt with mods similar to the ones you'e got. I've seen mechanics not be able to instal a CAI since it's not something they deal with often, or ever.
The term "aftermarket" is quite broad. Most replacement parts that you buy at NAPA or Autozone or whatever are considered "aftermarket" as they are generally made by a different manufacturer than the parts that were installed at the factory. By "aftermarket", do you mean performance-enhancing parts or non-OEM (non-dealership) parts?
If you're referring to performance parts, that's a separate issue. Most mechanics install only direct replacement aftermarket or dealer parts, not "performance" aftermarket parts.
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