What is involved in creating a Mashup site w/ Multiple APIs?

I have been reading quite a bit on mashup sites that use multiple APIs to create a unique offering, but generally speaking these sites tend to be utilizing APIs of differing types …Twitter, Goggle Maps, Pricegrabber …etc.

How complex is it code for multiple like type APIs …more along the lines of Amazon, eBay, & Shopzilla. Obviously Shopzilla is going to generate content from Amazon & eBay, but is it possible to negate these results from Shopzilla the and replace them with the results of the Amazon API & eBay API ?

The reason I even ask is due the revenue structure of sites like Shopzilla, Pricegrabber, etc. you are generating income related to clicks, but in the event that being an affiliate directly with Amazon & or eBay is more financially rewarding I am wondering difficult it would be to splice these results in with the results of the price comparison results? At the same time negating the results from Amazon & eBay to prevent duplication.

Sorry if the question sounds a little bit convoluted :slight_smile: