Absolutely no doubt, there are more con activities carried out by 'Christian' churches than by obeahmen/women. No argument there.
Remember though, 'Christian' preachers were condemned by the early Rastafari even more than obeahmen, if anything.
Maybe I am not really well-informed about obeah, certainly not outside of Guyana. But in Guyana GENERALLY the impression you get of obeah from peoples' stories and so on (those who believe in it as well as those who don't) is that it is often (not saying always) used for negative purposes,that practitioners tend to be motivated by financial greed, and that there are a lot of confidence tricksters in the game. As opposed to cumfa, which is a mostly-Kongo-derived tradition in Guyana, involving possession by various spirits for purposes of healing, a very African tradition with few Christian additions. Cumfa might be looked down upon, especially by middle- and upper-class people and 'holy christians' who want nothing to do with 'primitive' Africa (the same people who look down on Rastas)... however I've never heard people talking about being ripped off by cumfa people, or having a nasty 'wuk' put on them by a jealous boyfriend or whatever, through Cumfa. So it SEEMS that obeah lends itself more to those type of practices, and cumfa does not. Then again, I'm relying on second-hand accounts so maybe I should just shut up about the whole thing. The main point I was trying to make was, there may have been reasons why the early Rastafari condemned Obeah, other than Biblical fundamentalism and disrespect of African traditions.
On a personal note, I once thought somebody might have 'put a wuk' pon me, but now I think that was just self-delusion and an attempt to blame some external force for my own shortcomings.