Not all online classifieds sites are created equal. And it is important to pick one that have the features that best fit your needs.

Free Classifieds
Firstly, most classifieds service should at least provide free classifieds, then a paid version of the service which more exposure or other value added feature.

Registration
Secondly, does the classifieds service requires registration to post an add? For starters, there are pros and cons for site registration. Yes it might take extra steps before your beautifully written ad appear on the web, but the registration is essentail because of few reasons.

A: Non-registration encourage spamming of classifieds ads. Especially those of the medical kind that promotes enlargement of a particular sensitve organ. Now, imagine your ads buried under those spam! Not worth the effort.

B: Registered accounts on most classifieds service allows user to list their different ads under the account profile page. This is extremely useful for small business providing numerous service and products.

C: Most registered account will only need one centralised login username and password to access all the posted ads. Non-registered ads requireds one password and URL for each ad. A pain to remember them all!

Category of Ads
Thirdly, does the service have the Category that best describe the services or product you have? If yes, it will be generally be easier for users to find your ad.

Readability
Fourthly, is the site designed for readership? As in are the ads given enough screen real estate that can capture the reader's attention? Does the font and size encourage reading? If you find them too difficult to read, chances are so will your potential customers.