A < 1% conversion rate is quite bad to begin with. But I may be wrong and there might be niches where conversion is that low.
Have you checked your competition? Sometimes it is not about your website, but simply a competitor has improved his website or has some special offers. Most users check two or three websites before deciding where to buy.
So I would check the competition. And I would definetly let a third party take a look at your website with a < 1% conversion rate you have lots of space for improvement - at least in most markets.
Have you checked how visitors from other search engines convert? Any changes there, too?
By the way - you are right, Google traffic converts pretty badly compared for example to Bing. My conversion rate from Bing visitors is double the rate of Google visitors. I wonder why this is.