What you might do is find a drug store with a 100% satisfaction policy. That way, you can try it and if it doesn't work you can bring it back. I work at a Walgreens and we have people bring things like that back all the time (Epi-Stop was out most popular return for a while, many people got chemical burns from it).
Just ask before you buy. If a product doesn't work then the store can usually send it back to the company for a refund. Generally drug stores have a seperate cosmetics counter, ask whoever is working there because they will know the store's policy on cosmetic returns. We have a 100% satisfaction policy on all of our cosmetics items, even if you don't like the color, it's really a wonderful thing.