How much feedback do you have?
You can use someone's power seller status against them with your marketing style, so long as you have an established account to give the buyer enough confidence to purchase from you.
A lot of consumers prefer to buy from smaller sellers rather than larger sellers, so you can try to exploit that avenue in your copy, and this is where some creativity comes into play.
Take a look at your competitors marketing, look at it from a buyers perspective, not from a sellers point of view. Look for areas that you as a buyer feel are lacking and focus on how you can make those areas in your copy better.
A very common mistake made by online sellers is that they look at the product they are selling from their sellers perspective, but a sellers and a buyers perspective of the same product can quite often be very different.
What the seller thinks is important for them to say about the product, isn't always what a buyer is always wanting to read, and this can often be exploited by smart marketing.
When you sell anything, online or offline, the first thing you should ask yourself is....if I was a buyer, what would make me buy this product?