Read from books
Rules:
1. not researched, not buy
2. not within budget, not buy
3. not necessary, not buy (accessory)
So
1. need to know which model and brand you want
2. check price on internet , eg. Nikon
http://www.dchome.net/viewthread.php?tid=181018&page=1&extra=#pid2014542
3. check price at shop and compare the gifts (some gift are useless, select carefully)
4. check the camera, on/off, all function keys, lens, shutter
5. For DSLR, take one pic in all white, one in all black, check dead spot at LCD screen
6. For zoom lens, check if it zoom smoothly, focus working
7. Check accessory with kit is all there
8. Check the serial number on body and lens against the one on box/ warranty
9.Check warranty, need chop from shop?
10. proper receipt from shop
11. Ask for gifts, discount
12. usually need to pay cash / EPS, credit card with surcharge.