When we talk about PG having a poor concept of the value of items, we’re usually talking about packs, but this is also a good example. Many items are grotesquely overpriced - whether it’s packs in the store, for cash, or in this instance, resources in the trading post, for sigils.
I genuinely don’t understand a model where anyone engaged enough to be a regular spender is also informed enough to see the poor quality of the offers. It seems like there would be far more logic in offering good value for one’s spending - be it spending money or sigils - in order to encourage further spending.
I would suggest far better exchange cost/benefit ratios, and, for the trading post in particular, other players have hit on a concept that has been floating around for a long time: Let players get rid of things they don’t want, in exchange for things they do want.
Everyone wants rubies, sigils, etc., but people would love the chance to exchange unwanted spells, resists, shards, etc., for items that they need, even at fairly steep exchange rates.