Hopefully. But maybe not tho. Just some advice from a guy who used to run a music store.
Call first and ask them everything you want to know. Can they do it on the spot, can you watch, is there a flat rate... might as well find out everything before you waste your time going there. Are they helpful. Is the guy trying to end the conversation early or acting uninterested...
Give your business to the store that makes time for you no matter what age you are, treats you with respect and is completely truthful. If you ask a question and the guy guesses the answer instead of finding out for sure, go somewhere else.

Unfortunately, if the store is like any typical music store, they're not going to have time to do it right on the spot because there'll be other customers and other things that take priority. (lessons, other customers, repairs, calls, messages etc...)
It's also in their best interest to not let you watch them do it. That way they can keep you coming back as a repeat customer.
Watch the price. Some stores will charge you $60/hr to work on your guitar so make sure they have a flat rate and pick out the strings yourself. (some stores will push strings on 'special' that are actually bought off the grey market and are already half dead.
Never believe anything a salesperson tells you. It's their job to move merchandise and they'll say anything to get the highest commision or move a crappy item that's been sitting in the store for 6 months.

Best time to visit the store is not first thing in the morning when they open or last thing at night just before they close.
Most music stores are really busy right when they open because everybody thinks that if you go early you'll beat the crowd. Unfortunately, 20 other people have thought the exact same thing that day and they all show up at once. Don't show up at lunch time because the staff will be stretched thin because half of them are on their lunch hour.
Best time to go in is mid morning in the middle of the week.
ie, 10:30 a.m. on a Tuesday or Wednesday. The Monday morning earlybirders have wound down and the staff is usually walking around with nothing to do, pretending to look busy.