In many ways, what a shop owner looks for in a wholesaler is not much different from what a customer looks for in a place to shop. And chief among their concerns is always going to be price. When it comes to retail packaging & store supplies, the issue of price is even more important than when buying product to sell. These are products that will never be sold to a single customer. They are accouterments, at best. While important, the wise manager will always look for the best deal he can get. If your current wholesaler can't do that for you, it might be time to look elsewhere.
No matter what price you're getting your retail packaging & store supplies for, it isn't going to be low enough to make up for missed sales. You need a wholesaler who has the stock when you need it. Granted, no business is ever going to have everything in stock 100% of the time. Even McDonald's runs out of french fries now and then. But if you're dealing with a company that is constantly back ordering what you need, it may be time to look at another company for your needs. Customers can be forgiving, but they are less so now than at any time in history. You can't afford to lose them because of your wholesaler.
Of course, your wholesaler should also value you as a customer. This means going above and beyond the call of duty from time to time. It means expediting your orders and not handing you excuses when they fail to ship something on time. It can mean a lot of things, but it can be encompassed in one word: service. Without it, no company can survive for very long. Don't allow you or your business to be treated like an afterthought.