i think your just over thinking things too much...

don't think about the prize, just think about the bragging rights and prestige it will give to you... Hehehehehehe... The prize is just a bonus...
Obviously mao bitaw he is sponsoring the photo contest to promote his store... With the opening of a lot of camera shops here in cebu any business with a lot of competitors will always look for ways to attract customers to compete... Og dili ka magparamdam nga ni exist ka nga store or product, sigurado yabo imong negosyo...
this has been done a lots and lots and lots of times already diri sa cebu by other camera shop store owners...

Anyways you are not obliged to buy anything at the store just to vote, to see the entries, to join the photo contest and definitely you are not obliged or is forced to join the contest...
This photo contest is a win-win situation for photographers who will submit...