You're going to need a few essential things in order to become a serious reseller who is also taken seriously by suppliers.
1.) Selling platform - eBay, Amazon, Niche Site, etc. (Preferably with proof of sales history)
2.) POSITIVE SELLER RATINGS/REVIEWS
* Protect your brand's dignity, identity, and reputation at all times! Value your customers to earn their positive feedback which will fuel your reliability, trust, and ultimately, sales/revenue.
3.) Profit Margin Research
* Only sell items worth selling based on high-profit margins after PayPal fees, shipping costs, drop shipping fees, tarrifs, etc.
4.) Federal EIN Number
* Most quality suppliers will require this verification from you in order to know that you are a legitimate business in order to comfortably sell you products at wholesale prices legally.
Best of luck to you!