I can help with this as I recently went through the process and got a bike fit prior to purchasing.
I had been riding an aluminum Frame bike for about a year. I always had shoulder pain immediately as I hopped on the bike. I even had a shorter stem put in, and I still had shoulder pain every time I hopped on it.
It was time for an upgrade!!
I decided to go to a bike fitter to tell me me my dimensions to make sure I get the right geometry. I was after a carbon frame with at least Ultra groupset, so I wanted to make sure I did in my fit ($$$).
I went to one of the best rated fitter (in the bay are). He was great but I had 1 problem with him. After chatting with him and about my shoulder pain, he basically said I should only get an endurance bike, since I’m not an experienced rider. He basically went on Google and looked at best endurance bikes, and had me fitted for one of them.
He gave me a solid range to pick from, so I went around and did a test ride that fit the geometry he recommended.
I just didn’t like it. I wanted to grow INTO a bike. I felt like endurance was just too soft and too upright. My shoulder pain stemmed from the older bike being too big for me, not because it wasn’t an endurance bike.
I went to a great bakeshop nearby and started trying some more aggressive style bikes. We made sure that it’s the right size when I was test riding and I LOVED it.
No shoulder pain!! I concluded that my old bike was just a few sizes too big for me.
I have been on my new race oriented bike for a few months now, and I have NO issues. I’m pretty flexible and overall in great shape. So I definitely don’t have a problem with more aggressive style. I just had to make sure it’s the right size.
I recently went to a different bike fitter to dial in my fit again and he made a few adjustments to make sure I’m good to go.
My advice is this: You can probably skip the initial bike fitting to determine what size you should get (save that money for a fit AFTER your purchase). Go to a good bike shop that has experienced people who can tell you honestly your size. Test ride at least 10 different bikes with different geometries (endurance, race, and so on) from a few different shops. If you like a few, narrow your search based on your goals. Make sure you LOVE to color, you love to bike itself, and most importantly you felt good when riding it. If you experience any discomfort or it just feels off, skip it.
Go home, sleep on it, then decide what you want to buy.
Don’t force a purchase. If you buy something you feel comfortable on, something you can grow with, and you absolutely love the looks of. That’ll be the bike for you.