Max miles on a used truck before you reach 'uncomfortable' level?S

Used trucks. that's really the only way now given a new truck with what you really need is 1/3 of the value of your house. So, a used reliable truck? At how many miles would you just say 'hell no' to that one and move on? they are stout vehicles as long as there's no factory defect flaws.....so at how high would you still buy?