a pet store probably woulden't want to let you handle one if you dont plan on buying it then and there. and as far as bites go obviously each snake is different, and some are more aggressive then others but for the most part bp's tend to be on the more docile side. Look at it like a dog, if its handled more and used to people touching it, it'll stay calm when being handled. but at the same time there are times it needs to be left alone (48 hours after feeding to allow digestion) and other times, look at the bp care sheet on the site for more info about that stuff.

1. DON'T grip it be very very gentle (curl your hands and let it move freely but don't let it drop if its moving through your hands just keep switching out your hands from underneath it to support its body, you'll know what I mean when you're holding one)

2. try not to grab the neck or head (its perfectly ok if its moving and rubs against you but don't try grabbing for either, it'll stress the snake out and it'll get very nervous)

thats basically all I can think of for now, i'm sure there will be a lot more replies after mine to help you further.