When on-line you have to be very careful about what information you give to companies in order to protect your privacy and avoid identity theft or fraud. For many websites (especially on-line shops) you would look for the padlock in your browser that shows the site is ‘safe’. Well this is where the common misconception is; just because the site has the padlock, it does not mean that the website is safe.All the padlock really means is that the information cannot be easily read in the journey from your computer to the website’s server (I say easily as no encryption is uncrackable) . It does not confirm that the site will not use the information they receive in the way you want them to or that they will not give the information to anyone else. The padlock does not automatically mean you should trust the site!
This is also the case in the reverse. If there is no padlock shown the website could be quite legitimate however it would mean that you data could be read by a 3rd party who may not be so trustworthy. I would stongly recomend that you never give credit/debit card details over an unsecured connection.
If the padlock, however shows an error this too can often be safe. You can check what is causing the problem by clicking on it, and sometimes the problem could be that you have never visited the site before that it is uncertain how safe it is. You have to evaluate the security to make a decision as to whether it is safe or not.
When I shop on-line I always shop from websites that I am familiar with and have shopped on before or that have been recommended from a trusted friend. In the cases where I have found a website that I have never used before, then I would only risk buying on them if they offer PayPal as a payment. For me, PayPal provides enough protection on those sites for me to trust them.