This is how I go about it:
I don't rent points because I prefer to purchase transfer points to combine with my existing points, then I can make and control my own reservation. I find someone on the rent/trade boards that has about the amount of points I need +/-, I PM that person and I make sure that the points they are advertising are indeed transferable and are for the appropriate use year that I need them, some points can't be transferred. (If they aren't sure of these 2 things, have them call MS to make sure)
I've used Paypal 5 times, personal check once over the last 10 years and have never had a problem. The 1st time I was apprehensive but I went on the boards, found a
DVC'er with the points and then looked up their posts and threads, start date, and what I saw made me feel comfortable that I was dealing with a reputable person.
Once they get the money, no matter how you choose, they call and make the transfer into your account. Immediately thereafter you can call and make your reservation. The only thing is that you will not be able to see on your Member screen those points you purchased and had transferred in. Only MS sees them, at least it's always been that way, even as late as May 2010. They will show up as used after your stay!
It's not as scary or complicated has people make it out to be, the 1st plunge is the hardest. I've met some very nice people (over the phone) doing these transactions over the years.
Another option depending on how many points you need, you could also purchase 24 +/-points directly from MS (one time transaction) and combine them with a points transfer to only get what you really need.
I've never negotiated price, I always paid what the owner asked, and it's been $10 a point every time. You can only do one transfer per UY but one year I bought 2 inot the same year, and no one said anything or charged me, I think it's a grey area!
Good Luck!