I put my replies below each question

Quote Originally Posted by IrishEyes View Post

i) If there is any import tax applicable, who is responsible for establishing the value, how and who it should be paid to?
Yes, the value is the purchase price plus shipping cost to Ireland. The courier is responsible to calculate, collect and remit to Revenue.

ii) Is it normal for courier companies to come back afterwards looking for it?
Yes

iii) Do the Courier companies alert customs when items come in from outside the EU?
The courier act as agent for Customs / Revenue so pass over all required data.

iii) Is it possible that this is some sort of scam where couriers may collect but maybe pocket it themselves?
No, but they do get paid a fee for undertaking the service

iv) Should he ignore the letter from FedEx, go to someone else or pay it after clarifying the actual value of the items without shipping?
No