I would define a "professional" as someone that has the proper tools, knowledge and experience to do the job right. Look at the pictures in my post #18. There is a lot of expense in specialized equipment there. Amateurs are unlikely to have those tools unless they dabble in framebuilding. And even if you have the tools you have to use them properly. Bending a frame combines strength with a certain touch. You pull on the chain stays to widen them and they don't go and then you apply too much and it goes too far possibly damaging them. When you are experienced you get a feel for hard (but not too hard) to pull. If it is a dumpster find you won't care but if it is a 50 year old Cinelli you will care a lot.

If your main tool to spread dropouts is a 2X4, how do you insure your whole frame is still in alignment when you are finished? If you have indexed shifting, do you care that your derailleur is aligned in the dropout hanger so it shifts properly? If you dropouts are not exactly parallel to each other, do you care that when your QR clamps the wheel that the pressure puts a bind on your wheel bearings wearing them out sooner? How far out of alignment any aspect of the frame is before it is noticeable can be a matter of debate. I like all of mine to be spot on. Your standards may be different. By the way, Its going to be a very unusual bike shop that has the proper equipment to spread rear dropouts so everything is where it is supposed to be when done.