If the silver dragon is a bit devious... the best "reward" is giving them more work - as in getting them to do something in your advantage, but with them thinking you are doing them a great favor.
DragonSage: Thank you for bringing me this dangerous artifact, I will make sure it cannot harm anyone. As a reward, here is a 100 gp and something you may find interesting.
Heroes: Oh?
Dragonsage: Yes. A map to the secret tomb of Ulfar the Mad. This ancient document indicates how to get there. It is said that this tomb is most perilous, but I'm sure you can handle it. Filled with treasure of course.
Heroes: Sweet! ... hmmm... this map was drawn recently. The ink is still wet!
Dragonsage: oh well yes, it's a copy, the original is , erm, too fragile to travel.
Heroes: seems legit.
Dragonsage: Good luck!
2 weeks later.
Heroes: We're back! And you were right, so much treasure.
Dragonsage: Excellent.... aaand?
Heroes: Except... there was this evil sword of evilness. It tried to possess us several times and keeps summoning demons at sunset... So... could you take care of that for us?
Dragonsage: Of course! You were wise to come to me.
Heroes: Why do we keep finding these horrible artifacts?
Dragonsage: The magic of old was most perilous indeed. But fret not, I have a reward for you - the key to the Ancient vault of the Dark Dwarven Duke!
Heroes: Awesome!