I was approached by people that want a developer with a certain expertise, but I'm not an expert in the matter. Should I adjust my rates, take the time to learn the technology and not charge for it or just charge regular rates and make sure they understand that I'm not an expert?
Yours is a common question! There are a great many factors you must consider when setting your price/rates. People tend to penalize themselves both when they are experts and when they are not.
SMARTSTART has published a guide specifically about Pricing that teaches people how to put the right price on anything you sell. You can get a free copy at http://smartstartcoach.com/smartstart-pricing/
It has helped a great many business owners. I encourage you to download it, read the whole thing (it's under 100 pages) and do the pricing assessments included in it before setting your rates.
As you'll see within it, "level of expertise" is not the most critical factor in pricing and your price is an important form of communication to your client. Hope the eBook helps you with this. -- Linda
I like Devon's answer. The only think I would also recommend is to consider affiliate or referral system. Create a network or entourage of complementary resources. This is called a Power Core Team in business networking. You make a pact that you will refer people to them in regards to this expertise, with the understanding that they will refer business to you in your area of expertise.
This allows you to give your customer exactly what they want (keeping the client 100% satisfied). In the meantime, I would keep an eye on how often this particular expertise is requested. If you find that many people are requesting this expertise, I would use the time to learn that technology (and not charge for your service as you are learning).
If you find that this technology is rarely asked for - you may want to outsource or refer it to someone in your Power Core team.
As you can see, there is rarely just one "best" answer. It's often a combination of things.