Tough question.  It's like trusting the car next to you on the freeway, you hope they are law-abiding citizens of the road but there's no guarantee. 

The same holds true on the Web, you have to take precautions, be alert, ask questions, and take nothing for granted.   There are good legitimate businesses on the Web, even though some may lead you to believe that they are all evil scammers.

Here are some tips to help:

Create a new e-mail account just for the  businesses with a " newsletter" or "join the club".  Give them that account. That way you don't have all sorts of e-mails coming to your home e-mail account.  And you can keep things organized and not lose out on potentially helpful information.  Here are some great free email accounts Gmail.com, hotmail.com or yahoo.com.

Always pay through a Secure Site.  Before you give your security information, you should have https:// in the browser at the top of the page. As to  http:// with normal pages there is security code  in that  little "s".  You can click the  Pay Pal  link to see an example of the https://.

Create a free Pay Pal  account, its very secure as well.  A lot  of businesses accept it on-line.

If you are in business or going into business offering Pay Pal can boost sales and offer choice! 

Read  payment instructions carefully.  If it's your first or second time purchasing something on-line, it can be very intimidating to make a purchase. 

They do often ask for your e-mail info when you go to make your purchase.  This is normal, they need that info to complete the purchase.

Use security products such as virus scans, firewalls, e-mail spam ware, and spy ware.  This will help protect you against identity theft and protect your computer.   Norton or McAfee are good, I have tried both and I don't have a preference.  Norton is what I currently use though. 

There is also some free services on the net.  One thing you should be aware of is that they eat a lot of memory which has a tendency of slowing your computer down.

You should have security stuff in place though, if you are going to make a downloadable purchase like information e-books.  Once you've download them, you can read them right away and/or save them in your documents to read later. 

Never give your pin or passwords to your accounts to anyone. 

Look for contact info, if you see no contact info, you should take your business somewhere that does offer their contact info.

 Going up!