Can really a buying keyword exceeds 1% conversion

Of course it can. 4% is a little high, even for a buying keyword, but you should be able to pull it off if your website is properly optimized. You just need to make sure you're definitely using a buying keyword!

There are a few factors to consider:
1. Your definition of a buying keyword.
2. Are you running a ppc campaign.
3. The product being sold.

All in all though I would say yes. I have sites ranking for buying keywords that convert a little better than 4%. I also have PPC campaigns that are closer to 25%. These are for true buying keywords. The customers only intent on searching is to buy a product.

Are we talking product, PPC, Adsense, what?

SEO is free (to my knowledge). How do you buy an organic keyword?

Of course it can be over 1% conversion...

It all depends on lots of factors, such as, is it really a buyer keyword, how much does the product you are selling costs, is it a good sales letter, what do you have on your landing page and how many visitors actually click through to the vendor page from your landing page...

I had promoted products that had conversion rates up to 10% in the past so I can safely say, its more than possible

I think he's talking about a "buyer keyword" converting, not "buying a keyword" that converts. And I'm not sure how you'd do the latter anyway, LOL. :-)

There are a lot of factors going into conversion statistics. But yes, you can convert at higher rates. Most of the time unless somebody is a conversion Master, you're talking 1-3% though. Really serious buyer keywords can go higher if the sales or affiliate review page is highly optimized for conversion on a very popular product.

It just depends on a lot of factors. But for the general question you asked, yes, it can convert higher.

But if you're using this "conversion rate" to make a decision about buying something for your use in marketing, be cautious, because those "conversion rates" can be related to how someone specific who knows what they're doing is performing their marketing. And maybe something not easily duplicated.

For example, just because someone says you can buy a website or a hot resell rights product from them that converts for them at 5%, there are many factors outside of your control that may weigh into achieving that number - and you may not be able to duplicate the other person's efforts well enough to match it.
(Just figured I'd extrapolate a little because the question was kind of unusual - hopefully nobody minds).

Anybody think I've got "hype-sales-letter-itis" on the brain? :-)