See if you can work something out with the owner. If he isn't willing to offer some sort of compensation, you could write about your experience on consumer sites to prevent this from happening to someone else. Give the owner a chance to come up with an amicable resolution first though.
I'd go with the newer property. With an older home, you're also much more likely to incur hidden expenses. These could add up to be almost as much as the new home depending on what needs to be done.
Good on you! Do you know anyone else who owns buy to let property there? You should ask for a PM recommendation so you can avoid the hassle in the future.
If you don't trust your real estate agent, you should find a new one. Especially since this is your first home purchase. You should also bring along someone you know who has bought a home before for assurance as well as a second opinion.