Any discounts you receive have the potential of being either extra profit for you or additional savings for your customer. It’s a winning situation either way so don’t hesitate to ask for a discount.
I have found that the major chains have differing policies. One chain flat out said no, that they do not offer contractor discounts while another said they would sometimes discount very large purchases. That let me out on both counts!
The smaller chains and small independent hardware stores will be more willing to talk since these stores have local ownership and more flexibility due to their higher margins. They will probably be willing to give you at least 10% off. I suggest you approach them when you’ve got a large purchase on your cart.
Some suppliers will allow you to make purchases on account. This can be helpful for a couple of different reasons. First, this will give you 30 days to pay and maybe even a contractor’s discount. But also, this account will establish a history of purchases. This history may serve as proof of experience if you choose to pursue your contractors license. Check in with a local contractors licensing school to see what steps you can take to satisfy the experience requirements.