Pentax Smc DA 16-50 mm F 2.8 wide angle lens at Ebay

Hi all
Being a new comer in the digital photography after buying a pentax K20d body I am now without lens I do not want to use the kit lens, while the DA 16-45 extend the other way I want to spend my hard earned money on the best zoom lens in my humble opinion -the pentax 16-50 mm F 2.8.
I have seen some nice impressive shots at pentax photo gallery from this superb lens.

Now a lens has come up on Ebay Uk which I would like to get.
Is there a easy way to test a lens for its performance like shooting a red brick wall, map, newspaper or one of those test charts available on Net at 45 degree angle

I am interested to know that when you buy a new or used lens what tests you carry out to check its performance for your peace of mind.

Many thanks for your time

Whenever I buy a used lens off Ebay (or anywhere else for that matter) the first thing I do to check its performance is go outside and take some photos.
If they look ok to me then I am happy