If seller would say in their listing something like:  I am sorry but due to my circumstances (be it living 100 km from nearest town, or having health issues) I am unable to post more often than about every 10 days, I would consider buying from them, provided I was not in hurry and of-course would not be marking their DSR down.  But if seller just states their handling time as 10 days, I would be hitting the back button.

With this particular seller they are a huge seller with nearly half a million listings. It would look a little silly if a seller of that size tried to put in some reason such as they are unable to post more often than every 10 days with the volume they sell.

Ebay have provided sellers with the ability to stipulate a handling time which is reflected by eBay in the estimated delivery time. There is really no reason why any seller, no matter how big or small, should then have to justify why they have a handling time of x number of days.

When buying of websites it is not uncommon to have to wait three to four weeks for delivery. Customers accept the terms and conditions of those websites and consider it quite normal to have to wait for a few weeks for their purchase. It shouldn't be any different on eBay if a seller has stipulated a handling time of x number of days.