I'm kinda new to this so I'd appreciate some help.

I'm looking for a set of wheels. I have the TSW Snetterton or the MSR 093 in mind. Both are staggered. 20x8.5 front and 20x10. I've talked to a few dealers and they are telling me that I can't go 10 inches wide in the rear. Is this true? I've seen many IS's with these rims on. I was wondering if they fit and/or were hubcentric spacers needed?

Thanks for the help.