Use their tendencies

If the characters have shown themselves as people motivated by greed? Use it. Offer grand cash rewards for questionable quests. Have Lord Macbaddy offer them a lot more gold if they leave him alone. If some parts of the party has shown themselves susceptible for the lure of gold, they have given you a simple and useful lever to drive them. I don't know your GMing style or your players, but some inter-party friction can promote some nice roleplaying.

Abuse their tendencies

They are liable to haggle for every gold piece? Well, quest-givers are people too, they can say no. they might even get annoyed and actually lower the reward the longer they try. Or they simply won't pay them afterwards. Or it turns out the priceless diamond they are paid with is glass. Don't be afraid to pull tricks on your players, as long as you give a way or an opportunity for them to try and collect the debt/take bloody revenge I'm pretty sure they will be satisfied.

Disregard their tendencies

So they crave gold? Not all quests and quest givers can offer gold. A village of peasants won't have more gold than they offered, because that's all they have. Sure, if the party accepts payment in vegetables, they could shell out more, but cold, hard cash is not something they have in abundance. The strange wizard looking for ingredients won't offer the amount of gold that would buy even half the offered magic items. Make the quest reward itself, in the classic "you can keep what you find" manner. Or simply make sure that there are things they need more than gold on the line when they ask about the rewards (a favor, land, rank, survival etc.) and cut out the problem at its root.

Use their tendencies

If the characters have shown themselves as people motivated by greed? Use it. Offer grand cash rewards for questionable quests. Have Lord Macbaddy offer them a lot more gold if they leave him alone. If some parts of the party has shown themselves susceptible for the lure of gold, they have given you a simple and useful lever to drive them. I don't know your GMing style or your players, but some inter-party friction can promote some nice roleplaying.

Abuse their tendencies

They are liable to haggle for every gold piece? Well, quest-givers are people too, they can say no. they might even get annoyed and actually lower the reward the longer they try. Or they simply won't pay them afterwards. Or it turns out the priceless diamond they are paid with is glass. Don't be afraid to pull tricks on your players, as long as you give a way or an opportunity for them to try and collect the debt/take bloody revenge I'm pretty sure they will be satisfied.

Disregard their tendencies

So they crave gold? Not all quests and quest givers can offer gold. A village of peasants won't have more gold than they offered, because that's all they have. Sure, if the party accepts payment in vegetables, they could shell out more, but cold, hard cash is not something they have in abundance. The strange wizard looking for ingredients won't offer the amount of gold that would buy even half the offered magic items. Make the quest reward itself, in the classic "you can keep what you find" manner. Or simply make sure that there are things they need more than gold on the line when they ask about the rewards (a favor, land, rank, survival etc.) and cut out the problem at its root.