Hey!
I have just done both a Salar tour and a Pampas tour.
You can just book tours when you arrive into town, however be wary as I did the Salar tour from Tupiza, which was great as you get to see more and leave the amazing salt flat for the final day. However as there has been less tourists coming to Bolivia due to the problems, I was stuck in Tupiza as there weren´t enough people to fill a tour.
I eventually went with Tupiza Tours, had english-speaking guide/cook Archie and driver Reneku, who were both great! We were well looked after!
I dealt with Freddy at Valle Hermoso tours and he was extremely sleazy!! Kept putting his arms around me, which I kept pushing off! Not exactly welcoming behaviour when you are a single female travelling alone. He also lied right to my face about a tour leaving the next day, which was my very first question to him (to which he replied ´we have tours leaving everyday´), and when I returned an hour later to pay, suddenly the answer changed to ´no tours leaving the next day´ but he offered to take me out himself!! Of course whilst trying to grab my hands to hold onto!
As for pampas tours in Rurre, I went with Indigena Tours as I had other people recommend them to me (and Bala was completely booked). I had a guide named Tony, who seemed to have a big problem with me. At first I was unsure whether it was because I was of Asian descent, or maybe because he might have thought I was American (with all the problems between USA and Bolivia, plus I am actually Australian but don´t have a strong Aussie accent... but not an American one either!). In one instance after walking around in the heat for hours looking for snakes, he asked everyone in the group whether they would like him to buy them a cold drink from the next campsite (our bar was closed), everyone except me that is... and when I asked him why he never asked me if I wanted anything he basically replied with ´too bad´! ALSO he fed the monkeys, picked up snakes (one being a cobra which he brought back to the group, after he had caught it and carried it wrapped up in his t-shirt!!) and picked up a baby alligator. All this may sound very Crocodile hunter style and exciting, but it is extremely un-ecologically friendly. Animals should not be fed or handled.
Also heard from fellow travellers that Anaconda Tours went through a whole detailed itinerary with them, which turned out to be a complete lie, as they didn´t even have permits to go into Madidi Park and before the first day had ended they demanded to be returned to Rurre and then weren´t even given a complete refund!
Hope my stories have helped somewhat. :)