Buying from E bay is risky if its not a authrized dvt dealer. Dtv policy is not to activate receivers sold to you from another person and you'll have to buy a new access card, provide a respite and be transferred to a special team to get the OK to activate.
If the receiver is from a account that still owes Directv money you would have to pay off the balance before they let you move the unit to your account, all that said and Im sure some slip by but it can be a real issue.
I would only buy from authorized dealers, anyone else dose not have permission to sell the leased units and Dtv has no obligation to let you keep it. If the unit was owned you'll have less issues.
If I leased a car then tried to sell it to you on E-bay would you buy it?