Thank you. Whether you feel it is reasonable will really be up to you. I understand that you may not trust the dealer therefor from a legal perspective, you will want to obtain proof of the purchase and the amount. You must also remover that you will still have rights under the Consumer Rights Act.
Under the Consumer Rights Act, if you find the there is a fault with the item purchased then you can ask for a refund within 30 days, if you exceed 30 days but are under 6 months then you have to provide the seller to repair or replace the item, if they cannot do this then you can request a refund. If you notice the issues after 6 months then the onus is on you to prove that the issues were present at the time of purchase which can prove more difficult. However if the seller is not willing to comply with any of your rights under the Consumer Rights Act then you can enforce these by taking court action.
I will provide you with a helpful link which will allow you to find a solicitor near your local area who will be able to assist you with this matter.
I hope this information has helped. You can find a local solicitor who deals with this on the law society webpage which is;
If you require any help moving forward on this matter in the future, please do feel free to come back to us and I would be more than happy to assist.