Legalities of calling someone elses product a scam to promote your own?

I was wondering if there were any legal issues involved in openly calling someone elses product a scam. If a product name is trademarked, can you use it in titles on your page calling it a scam and trying to convert people to buy your product instead?

I know on public forums where people post there opinions, you can say whatever you want. But what about if you own a company and you're slandering another product on your site?

I've only been in the IM world for a couple months, I'm very new to all this.

Thanks for any answers.

There is no law stating you cannot unofficially label something as a "Scam", if there was a law to interfere with this then it would be against the European and US freedom of speech policy. However, you may still be liable to prosecution if you provide inaccurate facts or they are copyrighted. So far, I've gone crazy with insulting people and product publically and I've never been prosecuted, ever (the closest I could get was a legal threat from Microsoft).

But, if you make it official, you have to do it through the courts.

However, when you label it unofficially, your product must be an "alternative", not a "better version" or "update" of it or you by default have to pay royalties if it is copyrighted. You should check online if a product is copyrighted or not, the information is probably around somewhere as about 95% of everything on the internet claiming to be copyrighted probably isn't.

If they have no patent/copyright applied to their product, mock them, insult them or whatever and you will not get in trouble (unless you make it personal which can lead to harassment charges, so just blame the product, not the people).

Using the title "product name is a SCAM" and so on is ok, it is used often, but usually for affiliates selling this "scam" its ok to mislead, but not to go full out at a product saying it is a scam, unless it it really is a scam, most e-books, money making stuff, u can get away with calling it a scam. Everyone does anyways.