I'd talk to them about what they would be willing to do if you start wrecking those wheels due to your size. I say this because I am a tad over 30 lbs lighter than you, and I had trouble with the stock wheels that came on my road bike. I do commute often and not always on the nicest roads, but even when tensioned after the initial purchase I popped spokes on the rear wheel, and I pretty much knew I'd be spending some time with a spoke wrench whenever I rolled over any rough patches of road at an appreciable speed. Since I bought my bike online, I just took the plunge on some beefier wheels and haven't looked back since. If you're buying a bike from the store, there may be some sort of assurance they can give you so you don't have to spend more money on new wheels if you find the ones that come with the bike are inadequate. Just my .02