This is a common question and how do you know what is wrong, ask a bodyshop, they will sell you a paint job, ask a detailer, they want to sell you a buff job, buy some junk on an "informercial" and put it on the shelf and forget it. The site
www.autoint.com has numerous pictures and explainations of various paint problems and explainations of what cause them. There are "TSB's" from automanufacturers, Tech Tips from them and technical magazine articles written for professional publications on the site.
The photos and verbage are the same the company uses to conduct training for the OEM's new field hires that call on the dealers.
You can print them out and this could save you a lot of money and greif the next time you have to visit a dealer, bodyshop or detailer.
Hope these are of help to you.