When buying your iPhone 5, check for the condition as follows before you leaving the counter, if got defects, some can change some cant change, depends on your nego skill and luck...

Tools
1. flash light (handphone type) or under bright light
2. your eyes
3. calm and detailed mind
4. free time

Procedures
1. Check the box is completely unseal set, check is the capacity and colour you want, check serial and imei with invoice before open the box (if applicable)
2. check for any scuffs or dents at chamfer and edges
3. check for any scratches at front and back
4. check any chips at lightning dock area
5. shake the phone and use your ears to hear, some of the units have rattling sound, not sure is normal or not, using google they say either is loose power button or loose battery, or is vibrator sound, yet to clarify

Power up the phone
1. check if any dead pixels
2. check if any back-light bleeding issues
3. activate the phone
4. test camera
5. check capacity, serial and imei code

Reminder
1. Reject the phone and demand a new set (you have the rights to do it before leave the store)
2. Explain how bad is it (as bad as words can say, dont angry, just talk with reasons) and do not accept anything that is not perfect when out of the box
3. Do not accept second best

if anyone have better ideas and checklist let me know i will update it