I am wondering if it is possible to customize the default InfoWindow that pops up when the user clicks on various businesses that Google displays on its default map (see scr
It is not currently possible to listen to any click event on the POI icons so overriding/modifying the info window is not possible.
File a feature request asking for it.
i don't know customizing the functionality of infowindow, but by using google infobox we can customize the look, from that you can try the functionality. because infobox uses pure html code.
http://google-maps-utility-library-v3.googlecode.com/svn/tags/infobox/1.1.9/src/infobox.js