This is me! Haha. I have hair I can’t do much with. I actually really trust my stylist though and she promised that she’ll be able to have my hair keep the curls/half up/down braid I want. I think if you’ve got a good professional, they’ll surprise you. Plus you should have a test run style so that you can test out (go out the night you have it done! Or just throw a dance party by yourself). With fine hair, I think we all just are really down on ourselves about it but a true professional can almost always get you to where you want it.
I have long, fine hair too. I can hold loose curl in my hair day to day but it definitely falls throughout the day. My hair stylist suggested extensions. Not to add length, but for some volume. It will also help in holding the style. Also with an updo it won’t need to be super curly!
Same boat here and I'm probably going to grab some clip in extensions for volume. You can also use a sponge for an updo and they pin what hair you do have around it to hide it. Adds volume very inexpensively.
I also have long, fine hair. My stylist recommended I wash my hair the day before since "dirty" hair holds style better. She then put a lot of product in my hair to give it more thickness and texture and then she curled and teased it a lot. The end result held all day and night. She did a messy updo with a side braid integrated into the style. She had a hairpiece to add to the style just in case but she ended up not needing it. However, most styles you see on Pinterest use hairpieces and/or extensions to get the thickness, volume and/or length seen in the hairstyle.
Long, fine hair here too and zero curl to my hair. I ended up buying a ceramic straightener that actually has been helping keep some curl. I also bought some clip in extensions for volume. I used them for my engagement shoot and they helped keep my hair down and curled for HOURS!