My a4 has 17 inch alloys I have been offered 4 18 inch s line alloys for mine,will they fit ok and will they affect my car in any way?

 I am only looking at these because they look better than the ones on now ( Se Technik)

I have 18s on mine. I don't believe they were standard unless it was an option on an SE, I'm unsure though.  As for much of a difference, As long as you use the correct size tyre, it shouldn't have much of an effect. Obviously smaller side wall may make the ride feel a little more harsh.  My car doesn't look like it's on stilts or anything 😁 

The 18's should fit fine. Try it first though!?! Only thing you should notice is the speed on dash will be closer to the sat nav as the rolling radius will increase slightly. 

If they are in good nick and aren't to expensive they will be a good buy.