Jenny
Please don't listen to your friends.
The following is a quote from Google themselves in their policies and ad quality web page.
Link policies
These are guidelines for ad and keyword URLs and the website being advertised. Here are some examples:
Accurate Display URLs: Display URLs must use the same domain of your landing page so that users will know which site they'll be taken to when they click your ad; while a Destination URL can be different than the Display URL, both should share the same domain. The Display URLs within each ad group must all have the same domain.
Pop-ups: Destination URLs cannot contain pop-ups, pop-unders, mock system warnings or other windows that open automatically when you enter or exit the web page.
Affiliate URLs: Affiliates and other advertisers cannot use Destination URLs that automatically redirect to another website or that act as a bridge page.
What that means is that you can advertise affiliate products BUT the destination url must be the same as the link url.
Display URL
Your ad's Display URL is the website that is shown to customers with your ad. In standard text ads, the Display URL appears as the last line and is in green.
Your Display URL must accurately reflect the URL of the website that you're advertising. It should match the domain of your landing page so that users know which site they will be taken to when they click your ad.
Correct example:
• Destination URL: h(tt)p://www.travelingdog.net/toys.html
• Display URL: travelingdog.net
Incorrect example:
• Destination URL: h(tt)p://www.ebay.co.uk/travellingdog
• Display URL: (www).travelingdog.net
The brackets are just so the link bot doesn't kill this post
There you have it
You can advertise affiliate products
Hoping this helps
Eliot Proud