The difference between wholesale and retail is the amount of work to be done. We are a wholesale trade only supplier, but we don't charge less just because of who we sell to, we sell sell less than retail because we do less work than a retail signshop would selling the same products.
This all goes back to figuring out your shop hourly rate. If you are selling retail, your shop hourly rate might include (If you bill for 180hrs per month) 1/180th of your retail advertising budget, or 1/180th of the monthly salary of your graphics designer. I can't tell you what you should figure into your budget, but wholesale and retail sales are generally at two different costs to you and because of that you might decide to sell at two different prices - depending on how much work the buyer does.
For the amount of sales we do, a company our size might normally have 2 or 3 sales people, we have one because it generally takes less explaining and selling to sell at the wholesale level. They might spend $10k a month on advertising in one way or another; we don't spend even close to that. They might need to have a retail storefront that brings customers in the door off the street; we don't. A shop doing the volume we do might require 2-3 graphics designers, we don't really do graphics, so we don't really have anyone dedicated to it.
We also figure that when we buy a piece of equipment, we'll keep it running for 120+ hours a month. Many retail shops don't.
All these factors help us figure a generally lower hourly rate at a higher productivity than most retail shops. This allows us to sell at a lower price point.
Selling wholesale means partnering with the resellers to take on some of the work. Although we technically sell at a lower margin vs the gross sales, we probably take home about the same overall profit of a retail sign shop our size. This is because some we "share" some of our operating expenses with our retail partners.
So back out whatever cost you think your reseller is saving you, from a carefully figure retail cost, and that will give you a rough idea of what you should charge wholesale.