Your business is starting to grow, and suddenly you have interest from wholesale customers? What is the best way to sell to them?
There are several options, depending on your sales volumes, number of users and where your inventory is stored.
The simplest is just adding a discount code to your Shopify site, and giving it to your wholesale customers. They can have their own discount code that gives them X percent off at checkout. It works well provided they get a flat discount across all products.
Another option is to add a Customer Pricing app to your Shopify site. This lets you give preferred prices to specific customers. This option works well if you have one inventory store, and a limited number of wholesale pricelists.
If you have a number of different warehouses (or inventory in a number of different locations even if you don't call them warehouses), lots of different price lists, POS, and a high turnover, explore adding TradeGecko to your system. It can both control your inventory across all your different sales locations, and provide a website for wholesale sales through their B2B website option.