They were not greedy only, but they broke their promise to God. We should be aware then that the old testament laws still have validity in some respects. We should treat God with great reverence and not make light oaths:
Lev 27:9-10 ...all that any man giveth of such unto the LORD shall be holy. He shall not alter it, nor change it, a good for a bad, or a bad for a good
Numbers 30:2 If a man vow a vow unto the LORD, or swear an oath to bind his soul with a bond; he shall not break his word, he shall do according to all that proceedeth out of his mouth.