They all have more head and shaft options than a small pro shop. They also have a recognition from Titleist for the training they have received. Pretty sure they all have an electronic device for measuring ball speed, etc. That said, some will be more equal than others. They are not AI robots.
While some retailers may have the skills, they may also only offer indoor fittings. So my first preference is sites with outdoor fittings. Next is the personality of the fitter. Not all will be the best match for you. Not every golfer needs only new clubs for their best solution. In my opinion that is another reason to skip retailers. They do best moving inventory.
With options, I’d interview my choices to see which one may best matched my goals.

I think it kind of depends. Here in the Phoenix area we have a Titleist fitter that travels to different courses to do fittings but his home course is Corte Bella so anyone can set up a fitting with him at his course. Your best bet is to do some research and ask for references if possible. Be proactive during the fitting and don't just rely on the fitter. Look at the data, follow your gut instincts, be realistic in you needs (distance, forgiveness, height, feel). If after the session you are unsure or you had a bad day where you did not swing like normal, reschedule a follow up. Also back to your original question, the premier fitters for Titleist also have the full test kits where some general fitters at big box stores have a basic set of optional shafts to try so you might not get dialed in to what is optimal for you. Hope this helps. Any fitting should be better than random guessing and buying off the shelf.