I make websites for small businesses, and for some reason business owners love to have several domains with the same website but the TLD containing the city name.

For example:
1. smallbizname.com
2. clevelandsmallbizname.com
3. columbussmallbizname.com
4. cincinnatismallbizname.com
... and so on.

I've seen questions about localization per country aspects, but this is a much smaller scale, so I don't think the same rules apply.

The problem I have is the companies never want to write separate content per domain, just have the same website hosted several times at each domain. I feel this probably hurts SEO for two reasons:
1. Traffic gets scattered throughout domains, could be boosting just one domain.
2. Duplicate content penalty because the content is identical.

My question boils down to this... Should I redirect all the city domains to the main business name domain, or does having these separate sites help to rank better per city?

And if they are redirected, how does google rank the redirects?

Thanks for any input on this issue!!