You aren't ruining anyone's lives.  The thing about advice is: People can take it or leave it.  Even if you gave someone advice that doesn't go their way, it was ultimately their choice to follow it.

You aren't going to ruin the section by posting there.  It's there for people to openly seek advice; that's what you're supposed to do.  Even if you follow someone's advice, it's still YOU who has to solve your own problem.  It shouldn't matter where the path to that solution came from if it was still you who had to get there.

Don't feel bad just because you failed helping others 

Be glad that you at least looked to see what someone needs help with 

That alone is something I think everyone should be glad about

Its the thought that counts, as does the fact that if you at least reply to a topic the poster at least knows folks are giving it a look over.

 As to whether you post anything actually useful to the poster is upto them really. Even if you post sound, logical advice there is no garantee they will act upon it in the correct way.

The fact is, you at least tried to help. There is nothing wrong with that.