House Flipper

Here is a video with a quick explanation

(The video is not mine)

https://www.youtube.com/watch?v=7RKi6G2UgZ4

I just have one tip for this one if you want to 100% the game quicker, dont buy any DLCs before you get this achievement.
To get the achievement you have to do all the tasks you get in the mailbox, if you get any DLCs then the amount of tasks you have to do increases.

The same goes for the Game over achievement, but it is not alot more work if you got money