How would you safely backlink a web shop?

How would you safely backlink a web shop?

Hi, I got a friend with a web shop in a non-English speaking market and he has now asked me for some SEO help. I am thinking to rank the main page, as well as individual product pages. However, how do I go about doing the actual backlinking in a safe way? I don't want to ruin the poor guy's business.

I want to do this as safely as possible, but still do it somewhat blackhat. The main issue is backlinking the product pages, I need to automate this somehow, without using obvious junk. And doing it manually is simply not an option, due to the sheer amount of products.

So, anyone got any suggestions? Any ideas are appreciated, thanks!