It's definitely not a scam or ripoff, they cost nothing and I use them frequently. I have never actually purchased anything through them, so I don't think they charge a commission, though I can't be sure--as I understand it, they just make money by having you use your Visa card for the purchase. In this article[1] they tried to take it to an extreme, but frankly most of those tasks would be better for Fancy Hands.

Since I also have Fancy Hands and FH is better quality, I use Visa for tasks that are low priority, or I can afford to have redone a couple of times, or are very simple. Good examples of these include: not immediate restaurant reservations, basic research of all kind (anything from 'find me a place in NYC that sells Petrus Aged Pale Ale in bulk' to 'get me a list of all the language classes that NYU has for non-students with dates, times, location, and price' to 'how do I mail a letter to Spain'). Mostly generic things. Fancy Hands is what I use for specific, personal, or high-touch items--"Cancel my AT&T account," "Get PayPal on the phone again and again until they fix my account," "Please call this number in the UK during their morning and get this information so I don't have to stay up late," etc.

[1]: http://fourhourworkweek.com/2010/05/01/credit-card-concierge...