I'm not even a "professional" mechanic and I've seen first hand, and heard second hand of many many many instances where people buy aftermarket fuel pumps and they simply do not work. Ford, chevy, dodge dont matter. You need to buy oem. And that goes for anything electrical. You can cheat on some stuff but not major electrical components. They are just poorly made garbage that doesn't work. Same with remanufactured parts these days. You buy a reman starter, you may take it back 3 times before you get a functional one.
Why do you think a quality mechanic doesnt want your advice and charges you way more than your google price? That dude knows what's wrong and is buying top end parts. A good mechanic must stand behind his work, if you try to bring him parts to save money a good mechanic will say no. Because they need to be in control of the quality and part fitment so you dont come back with broken garbage blaming him, or the part just doesnt fit and now your car is blocking one of his bays where he needs to make money while he tracks you down to order the right shit.