Is it legal to copy content from a website?

There's absolutely no reason why you have to try and reinvent the wheel here in this circumstance. The reason why I use that metaphor is because the manufacturer made the product, therefore who better to describe the product, and since they've given you explicit permission to sell their products it's the same as giving you explicit permission to use their descriptions. Furthermore Google would not expect you to have to reinvent the wheel either. They're not stupid. They're not going to make you take something that's already perfect and change it make it less perfect just for the sake of it being different. This is why I like to say one very important guide every SEO should go by is the question what is natural and what is logical. It would be absolutely natural and logical for you to use the descriptions written by the producers of the products they have given you permission to sell.