leaking wheels

Afternoon all, hopefully someone can help me!!

When i bough my car back in feb, i managed to persuade the garage to put 2 new front tyres on it.

Since then, I have had to put air in about twice a week.

I've taken the wheels off and couldn't find any holes,nails etc so put them in the bath to find that that air was seeping out between the alloy and the tyre.

I took the car to quick fit who did try to fix it, but to no avail, so they reckon the only option is to refurn the wheels.

Now i'm planning on refurbing my alloys myself next week as wanna change the colour and they're starting to bubble, so have literally spent months and months looking at different guides.

Is there anything in particular i need to do to stop the air leaking between the tyre and the rim other than to sand the edge of the alloy and repaint??

Many thanks people!!