Most browsers warn you if a site is not secure, meaning encrypted. That may spook some people, but there is no real issue in just looking around. That does not mean that you need to get SSL (Secure Sockets layer) which provides end to end encryption, it is just a blanket warning.
You can still sell over it if you want to as normally the credit card provider or PayPal will provide a secure site.
So really it is up to you.