Don't know exact numbers, so I'll just make up some that seem plausible.
Purchase price of house $200,000.
Work house needs might cost $10,000
Person able to do that work wants to buy house.
If "Joe" does the work, seller (not me, close relative) pays "Joe" $10K, then Joe pays $10K as part of down payment, then Joe gets mortgage for $190K, is there anything illegal going on? Will the tax man agree that the house sold for $200K?
Owner/seller also has insurance, property tax, maintenance, etc. Can "Joe" pay these and seller credit them as part of down payment?