This is completely correct. There are false prophets and false teachers coming out of the woodwork like roaches, and they're almost as useful as roaches. Many of them do set patterns if their potential victims know what to look for. Questionable practices with offerings is one of the easiest ways to get a hint because they many times are slaves to the world, and that takes lots of money. Many of them also refuse to be transparent with Christian watchdog type organizations who grade ministries for the ways in which the offerings are used. There are also excellent Christian watchdog type organizations that keep up with false cults, false teaching, and failed prophecies from false self-proclaimed prophets. The Bible tells us these things will happen, and they are definitely happening. The Christian watchdog organizations are easy to find with a Google search, and I suggest that all Christians use them, ESPECIALLY before making donations. The most wise choice for your donations are local churches and charities you can see and check for yourself.
False teachers and false prophets are also DIRECTLY responsible for a huge amount of con games and fraud. SO, this is a very wise warning in many ways, especially considering that they deceive many in paths away from GOD.
THIS WARNING CAN'T BE GIVEN OFTEN ENOUGH! 
