I know it's an old thread, but I want to jump in here because it may be confusing to someone who's new to WordPress.
There are two forms of WordPress: WordPress.com and WordPress.
I believe the problem you're experiencing Ayush are related to WordPress.com, correct? The reason I say this is because WordPress
does not come with snap previews enabled by default
or at all, however, WordPress.com does (and I agree, those things are annoying).
Ayush, on WordPress.com, you cannot modify your theme code, add plugins, or do anything which would turn your blog into a commercial endeavor (it's in the
terms of service - make sure to read section 10 - Termination).
If I'm not mistaken, you cannot add any javascript to your site (not even using a Widget), but you may want to
contact WP.com support to verify.
If you're using the stand alone version of WordPress, then adding the merchant code shouldn't be too much of a problem; you have a lot more control over your blog and what it does.
In case you are on WordPress.com, make sure that you take every precaution not to have your blog shut down. I've seen blogs pulled for having a disclosure policy stating they may earn money from some of their adverts or blog entries, so be careful and back up your data often.
~ Teli