Hi,
If you do not want Google to see your site as just another affiliate site passing on traffic to vendors, then if you are using Wordpress, you can use the Redirect plugin.

For each affiliate link, you can make it point to a URL on your main site so the search engines will think it is part of your site. But the Redirect plugin will then redirect users to the merchant's site.

If you visit wordpress dot org/extend/plugins/redirection/screenshots/, you can see Source URL and Target URL. You can put a fictitious site URL in the SOurce URL box which is what the engines will see. But you can set up the Target URL to be your affiliate link which is where users will be redirected tol

Best
Raviv