None of my friends have painted their staircase and they do their own wall/trim painting so I am unable to get a referral. I can go to my local BM store and pick up a few business cards displayed on the counter but how do I know which person is best for my project?

I hired one painter from a store referral and she did a good job with painting rooms but not so well with painting doors (didn't brush in the right directions and left curved brushstrokes around corners; patching filler wasn't sanded down enough).

Any suggestions for how I should go about hiring someome?

1) IMO, Angie's List is worth the money to immediately screen out bad contractors.
2) Check the CCB number with your state licensing board and make sure they have up to date insurance (you should be able to check online)
3) Have them come over and get a quote. With stairs, some will spray and others will brush. Talk to them about your specific concerns (brush strokes, etc.). Ask them how many stair cases they've done recently.
4) Get referrals (preferably on a completed staircase job) and talk to those owners. Talk about the quality as well as the cleanliness of the job (was trash left all over the place overnight, etc.).
5) Ensure that the contractor is easy to contact. Often these guys are out pricing jobs while the crew is there (who may not have great spoken English skills).

Even after all this is done you will want to be there during the job. Be picky through the entire process. Prep is crucial. Do not accept shortcuts. If they know you're checking the work the temptation to cover something up is much less.

That's the number one requirement before you shop.