Front hubs, hence front forks are extremely well standardized. It'd be exceedingly rare to come across a fork or a front hub built to a differing standard. If your fork needs spreading it's a good indicator that something out of the ordinary has happened to it at some stage. Give it a CLOSE inspection before riding.
Apart from that there's nothing about the way the shop would approach this task that can't be replicated at home. The tricky bit is to bend both fork legs in equal amounts.
You could think that it'd be as easy as putting a threaded rod in the dropouts and simply use a couple of nuts to push them apart but you'd be wrong. What you need is a good line of reference, I've read of one guy who shoved a broom handle into the fork crown and was able to dial in the fork legs with reference to that. There are also various methods of extending a line from the steerer tube and check the position of the dropout WRT that.