+1 disclaimer point provided it is not in conflict with the law on unfair contracts.
See this
http://www.irishstatutebook.ie/eli/1995/si/27/made/en/print
The relevant extract is this "F
or the purpose of these Regulations a contractual term shall be regarded as unfair if, contrary to the requirement of good faith, it causes a significant imbalance in the parties' rights and obligations under the contract to the detriment of the consumer, taking into account the nature of the goods or services for which the contract was concluded and all circumstances attending the conclusion of the contract and all other terms of the contract or of another contract on which it is dependent."
IMHO consideration needs to be given to
bailment.
IMHO the repairer is a bailee for OP's computer.
Further, I consider the repairer to be a bailee for reward.
A bailee for reward has a higher duty of care than a gratuitous bailee.
A bailee for reward is obliged to take reasonable care of the goods in their custody.
If the bailee loses the goods
they will be required to prove that they were not negligent.
I see the issue of the courier as irrelevant to OP.
OP's contractual relationship is with the repairer.
OP is a stranger to any contract between repairer and the courier.
Repairer may have contractual rights over against the courier but OP stays out of that argument.
This appears to be a consumer contract for services.
Therefore, the issue should be within the limited jurisdiction of the Small Claims Court.
See this Citizens Information link FYI
https://www.citizensinformation.ie/en/justice/courts_system/small_claims_court.html#l0b797