Flyers are certainly an affordable way to advertise (versus other types of media). Keep in mind though that
they are time consuming and the return rate is likely down around 1%, but can be as good as 3%~4% in a specialized targeted market.
There is no specific result you'll get from flyers. It all depends on what you are marketing, who you're target market is,
the neighborhood, where you are placing the ads, and
even the design. Something like offering a 1-time 20% discount when showing the flyer. (just be wary of people that might copy them) Also a 'referral' discount, maybe $20~$25 of their NEXT detail (not the first one) when they give your card to a friend and write their name (and customer #) on the back. (Hey if it works for DirecTV it can work for you.)
If you start placing flyers on car windshields at a supermarket, I doubt you'd get a good return. But if you targeted areas of business like law offices, real estate offices, high rise parking lots (where people drive nice cars but are too busy to detail them), and distributed your flyers there, the return should be greater. Plus of course high end neighborhoods.
Cost is one thing that helps as you can get typical 'letter sized' pages done (in color) for under 15¢. If you're printing your own, and have a laser printer (single color) that cost can be down around <7¢.
But first take a step back and look at where u just came to get answers for your question... the internet.
Old school marketing tactics like flyers are not as effective as more targeted marketing but again, they'll work. Given their relatively low cost compared to other advertising mediums - I'd say go at it.
I'd say first get on search engines, the key is to have people that are looking for your services to be able to find you. It is the fastest growing commodity in the world.

Either do it yourself, or find someone that knows how to do if for you. (Barter perhaps as that's better than cash, ALWAYS!)
Don't even bother with yellow page ads and the like. No one goes to the yellow pages anymore, they go online. Learning to market online is a MUST for any business that plans on being successful in this day and age, weather u out source or learn the skills for yourself it is a must.
That being said, keep in mind that fliers, like direct-marketing,
often yield better results with consistency. I used to pass them out as a kid with my Dad, so much so that I could tell the manufacturer of the mailbox before we even got to it! :laughing:
Target an area and hit it once a month for several months in a row. Consistency is what ropes in a lot of people (
you either happen to catch them when they need your service, or they feel that your consistency indicates some sort of stability or professionalism.) Just think back at how many you've had show up on your doorstep and which one's you've not even looked at or thrown straight in the trash. Remember the design is critical here, then the consistency shows the prospective customer that you are a stable presence in their area. It'd be a good idea to attach a business card as well!
One more thing, remember that the mailbox is the property of the
US Postal Service and you cannot even touch it. You can *maybe* get away with taping a flyer to it, but it'd be better if you had a way to attach it to the post or the housing as a lot are brick these days. (The housing doesn't belong to the Postal Service, just the box itself.)
FWIW I have seem people that come after postman comes in a neighborhood and put their flyer inside. But that will likely get you a call from the local Postmaster and a stern warning! Better off if you take the time to put them on the peoples door. That shows a level of comittment that is much more than just driving by with a rock taped to a piece of paper and throwing it in their driveway.