eCommerce sites invest their advertising on Facebook Ads or Google AdWords?

Advertising expense

Facebook Vs Google AdWords

What is your goal?

Demand Generation VS. Demand Fulfillment

If you have a well known product (not brand, product) with a mature demand, focus your direct ad spend on search as the ROI is more definable.  If there is existing purchase intent, get in front of them.

Currently the massive benefit of Facebook Advertising is less quantifiable.

Social ROI = more than $$
Social ROI = $$+affinity/awareness/sharing/recommendations

If you have a product that is new or has some general differentiator, build a community (fan page) publishing relevant and engaging content to your target market, then educate your owned media source on why your product is important.  Do not over-advertise your product with news feed posts.

Looking at current trends for eCommerce the shift is happening from Google Adwords to Facebook ads as people would not directly search on Google for products they want they would go to eCommerce sites instead to search for the product they are looking for.

This is where the Facebook ads help. Facebook ads are more like TV ads where people hangout most of the time, where as Google ads are more of like newspaper ads where people just read them in the morning.

There are additional opportunity with Facebook in terms of not just selling or branding but in terms of customer acquisitions where people liking your Facebook page is eligible to receive future promotion.

Also Facebook ads are more engaging in-terms of different ad options including videos, gifs, carousel and others hence you can keep your audience engaged via different format without making them loose any interest in your product.

The fan page also act as a powerful medium to directly connect with your customers & provide them with customer support.

Apart from all these Facebook advertisements are cost effective way of reaching new audiences.