Money transfers for local guides

I have been doing some research for many months and have been working
through posts on the Thorn Tree travel forum.
We are looking to go to Rwanda and I have been
emailing Freddy Budaramani from Gorilla Select
www.gorillaselect.com We have negotiated an
itinerary and price and it is time to send some money
for the permits and 50% of the tour cost. I am happy
to do this but am worried about the secutity of
sending over money and if the money is actually going
to my tour and I am not the victim of a scam. I
dislike being untrusting but I have recently had
several hundred dollars go missing during a bank
transfer to the Bank of Tanzania in Arusha. There
seems to be quite a bit of discussion about these
types of concerns on the forum and I can see that
there will be some risk attached to these
transactions but could use some advise on the best
course of action. I did read
somewhere that the transfer can be done through money
exchanges rather than the banks which can take
several weeks.
thanks for the help