is wierd Gareth give me quest for 150 coin for 5 slime core but him or other NPC no give me the money for have fill the ask you have any idea how get the gold him or her promised on the NPC?
NPCs aren't reliable when they say they will give you something. Sometimes they say they will and they do. Other times they say they will or did and give it to you in role play, but not in game mechanics. If they don't, you can't make them give it to you. You can only ask and hope or cheat it in.
It's recommended to not rely on what they say. You're better off asking for an expensive item instead of money. You can sell it for 50% to Aldric. Or ask for several smaller items you can sell to the market. I once bought 50 turnips (not seeds) from Aldric at a low price per turnip (around 3.5 gold per)and he actually gave me 50. I sold them on market when the price was high. (15 or 16 gold per) Good profit. I don't know if I can get him to do it again since that was in an older release.