Wait, while the other replies have merit, I for one don't fully understand the question and so the follow on replies don't necessarily apply except for their specific cases.
What permissions did the item come with? (Have you actually bought an item yet or are you looking for someone to make the whole item?)
Is the item just for you or for resale?
For example, if you already own the item and it's modify, then you can texture it however you like, you don't need any permission from anyone, nor do you have to pay anything.
If on the other hand, you own the item but want someone else to texture it, then they can either do it blind, or there may be a resource such as a UV map which they would need. Whether that's available by buying a template, not at all or free from the creator of the original item will vary. You don't know if you don't ask.
I provide a full layered PSD including UV map for one of my items which I sell modify/copy/no trans, simply because i'm not the greatest texture artist and some of my customers probably have very different ideas to me, they're welcome to texture it however they like.