Website ads are becoming less and less effective as "ad blindness" becomes more prevalent. Ad blindness is the term used by marketing professionals to describe how Internet users are able to skip the advertisements and locate just the useful content. This has been a large part in the decline of Internet advertising as a viable marketing tool.
If your website is bringing you business, then I would recommend you avoid advertising because it may make you look bad. If your site is littered with ads it makes you look cheap and unprofessional. On the Internet, your reputation is everything. It is foolish to risk your reputation for a few pennies per click.
If the hits you get online are not converting into sales, then you need to start using your website to capture email addresses to build a private opt in, e-mail list. This targetted list can then be sent your advertising message as often as you like.
By all means, avoid ads but try to capture useful information from your visitors. With the power of permission marketing you will be better able to expand your business without endangering your position as a valued resource.