It is definitely better to keep posting trades rather than hoping to find ones that offer what you need. Lately, I have been bumping mine up to 3-star by adding 50-100 extra to the offer, and they get taken fairly quickly. It bumps yours up to the top, or near the top of the list and folks looking for what you offer will see yous first. Also, I seem to do better when offering about 5000, or maybe as high as 10k. Above that can take a while sometimes.
How good the trading is can vary between worlds, but we have more trading partners with Sentient than we do for regular goods.