Yeah, it's sloppy but happens all the time. If you can't find a box extension small enough to help, then the problem must not be that bad. What you do is put the device (outlet, switch, whatever) in the box in such a way as to make up the difference. The devices don't have to but up against the lip of the box, so long as they are properly grounded and the screw terminals are inside the box. Screw the device screws into the box until the face of the device is just about flush with the drywall. Then put on your plate. If the device sticks out too much, take the plate off and adjust it. If the device is too far in, take the plate off and adjust it, making sure that the terminal screws don't extend past the edge of the box. If there is such a big distance that the screws that come with the device are too short, buy longer screws. And the plates never touch the box. if they did, the plate wouldn't sit against thew wall properly. There has to be some little distance so the plate can sit flat against the wall.
Of course, if the whole thing is unacceptable you could make the electrician come back and redo the job. but he'll have to break out the sheetrock and then you'll have to have the sheetrock guys come back, and it'll be a mess. Just try to adjust it yourself.