When I search for my answer I get so many different opinions that I start getting confused I'm going to start a shop which is related to my site. What is better to choose start the shop on a new domain domainSHOP.com, on a subdomain shop.domain.com or domain.com/shop. Thanks for your information.
I'd use domain.com/shop, depending on your host's possibilities. If you can't afford it, then a new domain.
In terms of rankings there is no diference and domain/shop is easier for most people to set up. Just remember that if you are planning anything risky SEO wise (like link buying), that domains can pass penalties to subdomains and sub folders, sub folders can pass penalties to domains and sub domains but subdomains DO not pass penalties back "upsream"
Completely depends on the type of site you want. If the site is going to have other things aside from a store (blog, main site, forums, user registration...) then you may want to register the main site's brand (domain.com) and then place each individual area at the subdomain for the site (site.domain.com, blog.domain.com). This is what I do on all of my sites and it helps organize things a lot. As for SEO, there's no difference... really just preferences.
The main site is currently informational and has a good google ranking for it's subject, now I want to start selling stuff which is about the domains subject. I can setup anything (folder, subdomain or new domain) but if it's does not make a difference in SEO only if I do negative stuff, I might settle for a new domain. Thanks
Since you already have the domain that ranks well, I'm guessing adding a folder would leverage your current good rankings. A new domain will definitely not benefit from your current domain. And as far as I know, a subdomain won't benefit either. However if I'm mistaken, I'm sure I'll be corrected which is why I love this forum. I'm always learning more. Cheers, Drew