Most all of the offers are on the up-and-up.  But, always keep your guard up and always read the fine print!  A very few offers come with surprises that may turn out to be a headache for the unwary.  In my online travels I have run across offers that seem too good to be true until you read the fine print.

Here are a few snags to look out for:

• Offers that state in the fine print that you are signing up for some sort of service (usually voice mail, or the like) that will be billed on your telephone bill (yes, they CAN do this – even if you give them the wrong number! — they'll look you up and "correct" your obvious error (smile))   This practice is called "cramming" you phone bill (though in most cases YOU are actually signing up to be billed if you read the fine print.)  You can read a bit more on cramming here (FCC link.)  My advice is to always read the fine print and call your telephone service provider (AT&T, etc.) to "Block Third Party Billing" (beforehand.)
   

• Offers that are "free trials" that charge you some nominal fee (like a buck or two) during the trial period but if you don't cancel within the trial period you will be charged full price (usually a much greater cost) or that your credit card will be billed on a recurring basis until you cancel (Argh!)  Again, read the fine print!  Some free trial offers may make it difficult, laborious, or impossible to cancel.  Watch out!  Free/low cost trial offers that turn out to be extremely difficult to cancel (some customer service numbers run perpetually busy, or put you on hold for hours, etc.   …or some web site based cancellation links just lead you to an "error".)  Read the fine print.  Save all copies of emails you receive.  Print out any specifics such as login info, account numbers, offer agreements and terms of service (TOS), etc. that are presented on the screen.  Print and keep a hardcopy file of all confirmation screens and emails!
   

• Offers that ask for credit card or other private financial information without presenting you with a secure server.  In Internet Explorer, you will see a lock icon   in the Security Status bar.   The Security Status bar is located on the right side of the Address bar.  The certificate that is used to encrypt the connection also contains information about the identity of the website owner or organization. You can click the lock to view the identity of the website.  If you are being asked for any private financial information without them taking minimal precautions to protect that information (by using a secure connection) then move on – don't give them any information!
   

• Cell phone offers that have you enter your mobile phone number, wait for a text (sms) message containing a pin number or password, and then have you enter the number in back on the web site.  They will call this "confirmation".  Usually, what you actually are doing by confirming your pin number is giving them permission to add you to a subscription service that will bill your cell phone account some amount ($9.99, $15.99, $29.99!) on a regular basis until you cancel.  Always read the fine print!  Know what you are signing up for.  To avoid costly mistakes you may want to contact your mobile phone service provider beforehand to see if they offer some sort of subscription service blocking / 3rd party billing blocking service (beforehand.)