Ask HN: Would you do some free work for good?

I am thinking about a match-making service for developers/designers/whatever pros and for their potential clients or charities. For example, you are a great developer and want to help some charity for good. Let's call the service FridayForGood. So, you signup and show your expertise in your profile and your availability, say, next Friday, or first Friday in next month. Some charity or may be your potential client (but without obligations I suppose) sees your message on the board and thinks your skills would help them and their showcase the project to you so that to make you interested.

You choose the one that interests you the most and contact them, then give them 8 hours of your mad skills for free. Then, if it's a potential client, they can continue working with you on a paid basis. If it's a charity, they just thank you and you still can consult them or help in any way.

So, the question is, do you think it would be interesting for both sides? Would you use this service as a client? I know there can be speculative bad guys searching for free labor, but I think it can be quite easily filtered technically. Please share your opinions.

Thanks!