Well, I am sponsored, mostly because I created my company lol. 
But the responsibilities are the same. You gotta do what you gotta do to put your company out there, represent it the best way you can. However, the responsibilities for any owner include:
Checking/making CAD work and verifying the accuracy and weight distribution of the yoyo.
Contacting your machinist and anodizer and part makers to get a sense of the cost needed to make the yoyos.
Testing/assembling the yoyo’s, nitpicking vibe and ano flaws.
Shipping out the yoyos, wether it be to direct sellers or our favorite retailer, YYE.
And keeping the rest of the team in check. Without a team, a yoyo company isn’t a company. It’s more of a… group.
I remember once I was so stressed out I wanted to quit right then and there, because we had so much going wrong and so much going on at one point. But we persevered and made it out alive.
If you want to be sponsored, again, you have to represent the company the best you can. If the company isn’t for you, don’t accept, because you’re going to have to throw those yoyo’s like it’s the best thing you’ve ever thrown. Sure, you can use other yoyo’s in your freetime, contests (in the audience), but on stage and on camera, you are a part of the company, and you throw their yoyos.
That is all, gentlemen.