An Export CofA can also show the plane meets the published requirements of the importing country.
Note if the requirements are not published via ICAO they are actually guidelines – assuming the country it’s going to is an ICAO member – but many authorities will argue this unless you show a willingness to argue back.
GTS is right that some countries don’t have export CofA’s – whilst other countries don’t require them – but some countries do require them (and some require specific wording) – I even know of one country that requires an Export CofA from the previous authority whilst having no procedure by which they can issue one when the plane gets transferred from their register.
In short – talk to both authorities as early as you can on this subject.
Personally I always recommend obtaining an Export CofA even if the receiving country doesn’t specifically require it – cause you don’t know what the next will want.
Then again if your selling you don’t care where it goes after you got the money – do you?