Deferred maintenance is not uncommon, but of course it should be reflected in your offer.

When you later sell that investment if you sell for the same price you would be selling for $4 mil which means then that if you want to 1031 and defer all tax you would need to replace that with another asset worth at least $4 mil and use all $ 3 mil in cash in the purchase.Once you leverage up you'll have to stay at least at that level in order to defer all tax. 

As ordinary expense as incurred or defer the costs until the house is sold?

A property should be fully rehabbed with little to no deferred maintenance or CAP Ex.

My mother in law has a nice home in the county thats on 18 acres that’s worth about 120k as it stands and has a value of about 180k after 10- 15k worth of needed repairs/deferred maintenance .

Several Turnkey providers I've been investigating recently are pretty aggressive at addressing deferred maintenance upfront, often opting to replace HVAC and roof which technically may have a few more years of life left.

That sounds like a good buy if there isn't any deferred maintenance, though I don't see anything for lawn care. 

An alternative is that they could have had their taxes deferred, which allows them to pay whatever whenever.

You can defer taxes, easiest way to think of this is trading up.

When you see a lot of property and get used to analyzing it in a given market, you'll know what's "normal" and then when you see a pro forma that shows 30% expenses, and you'll know its a lie straightaway, or you'll see a low maintenance number, and that could tip you off to deferred maintenance.