How much reliable Google's Geocode Web Service

My site is using Google's Geo-code Webservice to get latitude and longitude of a address and based on returned coordinates, it is calculating distance between this and another coordinates.

As I feel that Google may return coordinates based on only city even though user enters in-correct address. I am calculating prices 开发者_StackOverflow中文版based on distance between both points and these are in 0-50 KM.

Can anybody tell me how effective is this as I think it may return incorrect distances.

Is there any other way to do this ?

Yes, if the user enters an incorrect address, it will return a more general coordinate. However, the response from the service also contains a flag indicating that the match was only partial.

Check for partial_match under Results

http://code.google.com/apis/maps/documentation/geocoding/#Results