I have always dealt with vista print and have never had a problem, all the way through the checkout process they try to add stuff to your order, just make sure your not adding something you don't want.
And make sure you start receiving their emails before you order anything cos chances are you'll get what ever your wanting for free, just pay the p&p.
My cousin owns a printing firm and even he says for me to get some stuff from them cos if it's free and good quality you can't go wrong.
ps you can add 5 free items per order.