As far as the fight being fixed- as was alluded to, there's probably not much need to really put a fix in when a guy's just out for a quick payday before he retires. Happens all the time. You have to realize that those punches near the end of a guy's career are really fucking up a guy's brain. If you get clocked pretty good near the end of your career then you should do the smart thing and stay the hell down. No need to take shave a couple of IQ points off just for your pride. Look at Riddick Bowe- Golota practically turned the guy into a retard over the course of what, 2 fights? (There were some analysts who literally felt that Bowe was punished so severely in those fights that it caused serious brain damage.)
As far as Tyson not taking anything- I seriously would be surprised if Tyson was not taking anything. I've read of people being on vacation in Hawaii, out on the beach partying, and the guy- in training camp right before fighting Lewis- walks up to them and starts partying and smoking pot with them. He doesn't sound to me as if he's too worried about drug testing (or even taking training very seriously for that matter).
Hell, even Fernando Varga tested positive for steroids. Look at that guy, he's built like a tennis player at best. Those guys have to do a LOT of endurance work.
Look at Chuck Finley, a baseball pitcher who's ex has claimed she saw him injecting steroids and said he bragged about how easy it was for him to beat the test.
I can also tell you it's pretty obvious that certain football players who have mysteriously extended their careers beyond normal expectations are juicing as is Barry Bonds.
Also, something else funny: I remember, I guess it would have been a few years ago now, that on the Howard Stern show they were making fun of another guy Tyson was fighing and his big fat titties. Between those two guys, and all the requests for matches with Butterbean and Tua, Tyson could make a career out of just fighting guys with tits.