If you are refering specifically to the spells on this site; some do, some do not. Why is that? Because not everyone whom posts spells knows how legitimate magick works and rather instead, perpetuates fantasy garbage. Many legitimate practitioners post spells, forums, and articles however. But even then, if a spell works can depends on many factors! But for that I'm gonna go ahead and drop some wise words from Miss Weatherwax below along with some from Miss Lark.
That's the thing about the internet- you're trusting strangers. So be cautious about the spells you read and don't expect them to always work. But once you get a hang of spell work and what really works for you, you'll find ways to alter them to.work.for.you and you'll be able to better identify which ones will not work for you.