Google ads spend into cash question

Let’s say you have the ability to spend with Google Ads for free. What is the most efficient and low-risk way to turn that ad spend into real cash. Ideally avoiding complex niches like forex/gambling which require strong tech setups(white page, cloak, etc)?

I am even ok with negative ROI.

If so, then best way is as an SEM agency.

I'd tend to agree with @FocusFocus but BH niches are obviously more profitable - although they require strong tech setups/cloaking, as you mentioned.

But yeah basically SEM, and anything that is marketing related. Perhaps if you have a store with normal products/stuff (WH) that's also something to consider.