A friend of mine has the above. If he does a border run just before it ends will he get 90 days more when he returns.?

Yes, as long as he enters in or before the visas expiry date he will get another 90 days.

 

If he’s the spouse of parent of a Thai he can extend that 90 days by 60 days for 1,900 baht.

If your friend has been staying here (as opposed to leaving and returning) he should already have been doing border runs since each entry is only for 90 days.

Providing he does a border run and RETURNS to Thailand just before the visa expiry date, then he will indeed get another 90 day permission to stay.

 

Unlike Visa Exempts or Tourist Visa's he cannot extend his "permission to stay" by 30 days, although if he meets the conditions for marriage or retirement he may be able to extend for a longer period.