I have what I believe are the Zipp 530s (or had, as the front caught a branch and pulled out some spokes); I use what was the rear as the front now. I gather the 500s are 650s? Assuming that $200CDN is not like $400US these days, that's a good price if it's wheels and not just rims. I think I paid $500 for the pair, built up, a couple of years ago. They seem decent enough.

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"Go yell at an M&M"

One thing to consider is the gear setup. Meaning is it a freehub or still freewheel? If freehub, what options do you have for a cassette? The cost/limited availablilty of parts is a consideration.

I bought a Zipp 440 front wheel (tubular) this year (Wheelsmith built, chris king hub) for $200 US and thought it was a decent deal. Just for reference.