Throwing huge parties are costly from what I've heard. Especially if one chooses to use a party pack. There's 25k right there. And if one chooses to do a party hop and buy multiple party packs? There's all the food and drinks to make as well. And then prize bags if you wish... etc.
Some people like to help friends acquire housing or tools or whatever. Some people just like to craft a lot but not spend the time gathering the resources. Or trying to fill out that cubimal collection... 5k a pop with only a chance of getting the cubimal you want/need.
There's a lot of stuff currants can be spent on, depending on your mode of play. Granted, I think most high-currant spending involves spending them on others, but certainly not all.
Wait, what exactly was "sold" here? Currency? If I sold currency (clear violation of TOS), I would not announce it on the official forums. So I will give the OP the benefit of the doubt until I understand what is being sold here...
"Except as expressly permitted through the Service, you agree that you cannot sell or otherwise transfer any of the Credits, Currants or Items, or any other content or information included in the Service to any user or other third party, including on Internet auction sites (e.g., eBay) or in return for anything of value (including "real" money) or otherwise."
It was likely 250k currants for some game item, as the primary post suggests that the undisclosed item was what was owned and up for grabs.
At any rate, it's not anyone's business but hers and her buyer's, and I'm sure if devs were concerned, they'd look into it after seeing the thread; they are very good about reading all the shenanigans around these here forums.
Wow, super cryptic. It's true that selling currants for RL money is against the ToS, but I'm guessing that Linnea was just naming his price for an awesome item.