Consider this fair warning: A set of discounts offered by Google for its new—and non-free—comparison shopping service are about to expire in the coming days.

In case you’ve been off the electronic leash in some tropical utopia of seclusion for the past few months—in which case I would like to offer my services as your personal assistant, assuming travel is included, and no smartphone or e-mail use required—you know that Google is replacing free listings on the Google Product Search comparison shopping service with paid product listings ads through a new online program called Google Shopping. This isn’t some slow-moving plan. This is happening now, and e-retailers have already reported sharply reduced traffic from Product Search. A full report on those changes, the reasons behind it, and what retailers can do to thrive in the new environment, will appear in the September issue of Internet Retailer magazine. In the meantime, you can read more here or here.

No one likes it when things that were generally free become things that generally cost money. You should have heard all the compound curses that I crafted when I realized that listening to the streamed baseball broadcasts from my hometown required me to fork over just a bit more scratch to the baseball-industrial complex. But Google’s having a sale, and you should know about it.

Here’s the deal: Google is offering merchants that create product listing ads by Aug. 15 a monthly credit for 10% of their total product listing ad spend through the end of 2012. Google also is offering merchants that now take part in Product Search $100 worth of credit toward their Google advertising; that promotion also expires Aug. 15. Merchants interested in the latter can find the required form at http://www.google.com/ads/shopping. Google won’t say how many retailers have taken advantage of those incentives; the company’s representatives will offer only that the company is “excited about the number of retailers that have signed up for Product Listing Ads since the transition to Google Shopping was announced in May, and about the range of products offered by these companies.”

Good luck with Google Shopping, and please remember me when you exile yourself to the South Pacific.