Hi sooeng,
frankly, I also don't know ... hahaha!
My own way of creating WTS threads - label subject explicitly so people (like me) can use Cntl+F to find things that I want easily (eg. Leapfrog, Graco). So I also create various WTS for different items. Logical to me, at least
<font color="ff6000">My assumptions of the various threads:
(i) WTS, WTB & Free Items = for mommies like you and me
(ii) Overseas Spree = for mommies to buy from US/EUR/etc because of SALE/cheaper option and everyone shares the int'l shipping cost
(iii) Bulk Purchase = for mommies to buy from SIN distributor by satisfying Minimum Order Quantity
(iv) Business = for business users who earns profit from each transaction</font>
However, it seems like BP is more of biz-thread than my assumption.
I've asked about the difference between BP and Biz threads
here but nobody answers me