I put fix in quotes because I imagine the repair is low quality.
That is OK.
Can you really pull a noticeable dent out of a metal door or quarter panel?
You could pull a huge dent out in sheet metal with a puller. To some extent, the bigger the better. A broader dent has less resistance. It’s not the diameter of the dent that matters as much as the severity. With a larger mild dent, the metal is not stretched as much. A deeper more wrinkled dent is going to be less successfully pulled out without multiple pulling places and lots of filling.
Are you talking about a do-it-yourself dent pull or a paintless dent removal done by a professional? I have used the latter before and they are pretty talented. They use a number of picks and other tools to bend the metal back into shape slowly. I had a 6+ inch wide dent taken out of a rear panel for about $150. The technician said that was about the limit of what he was willing to try. The result wasn’t absolutely flawless but it was close enough for me and way cheaper that the sand-fill-prime-paint solution.
Doing it yourself depends on your skill level. I have never had very good luck trying it.
Like Al Bundy says, it will work well with a big dent where the metal hasn’t been folded or wrinkled. But it’s usually just as easy to pop it out from behind, or even replace the panel. If you have an old car that is made out of thick steel you may need hydraulic equipment to get a dent out. But even with the thin metal, if there’s been enough crumpling, you need to hammer out the folds, use a lot of Bondo, or replace the panel.
If the paint has been cracked, you need to strip and repaint-otherwise the area will rust.
Seriously-do experience body mechanics really hammer out dents anymore? The time involved makes me think that it is easier to replace the panel, weld it, and repaint.
Do body guys use lead filler anymore?
My simple method for door panel dents that are not badly creased:
Remove inner upholstered panel (or enough to gain some access to the door structure. Insert deflated football (a child’s small football works great). Pump up the ball till the panel ‘pops’. Deflate ball, remove and re-attach inner panel. 
I’d guess most body shops would replace the panel for any major dent.