Thanks, I too have an old Oster electric trimmer, I think I purchased it in about 1966 - but it hasn't seen much service in the last 10 years as I purchased a lower cost package to get a set of stand-offs. The ones I had for the Oster have broken over the long years of use, but the motor and cutter on the trimmer still work well, best I can judge.
I don't plan to get into complete grooming, just touch up. I already use scissors to cut hair away from his eyes, around his ears and around his butt to keep his toilet activity from leaving a dirty rear. The Westie has a miniature Golden apron in back, and I though an electric trimmer may be the best/quickest way to keep that trimmed. Then I had the horrible image in my mind of getting my human trimmers stuck in his heavy hair. He an get unpleasant if I hurt him, I found that out trimming nails and hitting the wick on one nail, just a tinny drop of blood, but it apparently hurt and he struck out at me. So, a trimmer stuck in his hair would be a real nightmare.
A word of advice about PetSmart groomers - they are not professionally trained groomers unless things have changed an awful lot recently. Sure, while some of them probably ARE professionally trained, for the most part PetSmart feels that there are two ways to do things, the wrong way and the PetSmart way. When they hire a groomer, it's not mandatory that they have grooming experience because PetSmart would rather they NOT have their own way of doing things so they will be more open to being trained the way THEY want them to groom. They send them to THEIR grooming school, which is not truly a school at all but basically a couple of seminars where the folks learn how PETSMART wants them to groom dogs and not necessarily how they SHOULD groom them. I used to work for them and was appalled at some of their practices, their dog obedience classes are another thing that I don't agree with. I left after 8 weeks because I couldn't watch the things that were going on go on any longer. Anyhoo, on to the clippers...
Basically trimmers are trimmers. Some of the human ones come with little tiny head attachments now for shaving designs into the "whitewalls" on the sides of a short haircut, but the trimmers themselves and even the blades are the same. A word of advice, though, don't buy one of those sets that has one clipper/blade combination and a dozen different colored combs for leaving the hair different lengths. Those sets might seem like a good deal because of their low prices but the clippers themselves are AWFUL and don't hold up. The blades get dull and clog up and they're basically useless after one or two uses, if they ever do a good job at all. You'll end up buying set after set and paying who knows how much over time to keep a working set of clippers in the house. The oils in the coat will have those clippers useless in no time! Better to spend a decent amount for a good name like Oster (or an equally good name) and get the one with interchangeable blade heads. Get yourself two or three different heads for different areas of the body and you'll be all set. Keep the clippers oiled and you should be good to go for a long time. I have had my Oster clippers for about 30 years now and they still work just like they did the day I bought them. On the other hand, I could fill a small dumpster with those "cheapies" that people have given me over the years thinking they were doing me a favor because they no longer needed them. I turn them on and the blades don't even move, they just make the buzzing sound. It reminds me of Fred Flintstone shaving with a bee in a clamshell. :)
Ghilly
There are human clippers you can use on dogs but there are many different blades. I used to use a human clipper on my aunt's Terror mix but I just trimmed her whole body so no particular grooming pattern. Ask the groomer if you can watch and ask her what she uses. I don't know why she should mind. If you get stuck, I can ack a couple of groomer friends, most of my grooming was done on long hair breeds.