bought my wife repairable writeoff 2year old mazda 3 done 16k on odometer, all the parts and labour even had to bring a car from newcastle for parts ended up being about 10.5k. We didnt sell it but similar ones on ebay at the time (last year) were 15k+. This is with minimal effort from me. Had to drive around a bit for a few parts, call some wreckers and attend few auctions. If i was a pensioner this is what i'd be doing.
The only problem about making money this way is you're money may be tied up for about 2 months while its fixed and then you wait for the inspection. Then selling may be hard depending on how popular it is, one car can end up sitting 6 months in your yard or it could take a week. If you;re selling make sure you dont hide the information that it has a crash history as it has been written off and your lawbound to say it was. You can sell 5 cars a year without paying tax after that have to declare to ato