Decide the kill criteria first
Work out your break-even CPA. Spend up to roughly two or three times that with no sale and the product has answered you. Below that, you are reading noise.
Search first
If people already search for the category, Search tells you fastest and cheapest whether demand exists and what it costs. If nobody searches for it, that is itself the answer — you need demand creation, which is slower and more expensive.
One variable at a time
New product, new creative, new landing page and new bidding strategy at once means you will not know what failed.
The honest part
Most products fail. A test that ends quickly and cheaply is a good outcome, not a wasted one.