I once took my '74 VW bus to Canadian Tire and the young mechanic there needed me to come into the garage and find the engine for him.
I’ve tricked people with my Boxster on this. It’s got a front trunk and a rear trunk, so people are like “where the hell’s the engine?” 
Part of making an informed decision on this is getting to know your vehicle. Actually read the service manual and see what is recommeneded for your type of driving. I recently reached the 60K mile mark and transmission service was recommended. So what does that mean with my vehicle? Since it’s just a fluid change and the dealer wants $200 for it maybe I should just take it to my trusted neighborhood mechanic. However, since I actually know my vehicle I know it has a CVT and a little research shows that a propriatary fluid is used by Nissan so I’ll be taking it to the dealer. Now, a TNM would probably tell me that but a couple owners on the MB I frequent for my vehicle took the car to a quick lube type place and had them offer to do the tranny as well. Turns out the wrong fluid was used and warranty is now void. Another advantage of a dealer is they will have serviced a lot of your make/model/year vehicle. Have a strange squeek, rattle, etc? Bring it to the dealer because chances are they’ve fixed the same thing on the x many other models of that vehicle they sold and there may even be a TSB out for it.