When people sell websites they mention PR is this the best indication of site traffic?

Not at all

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MBM | Review your host | Know Vista?

It is one indiction because sites with higher PRs show up higher in the rankings but it may not be for the term you are looking for. There is no source for accurate traffic rankings though check Alexa Web Search

Actually, it would be better to run a search in Yahoo, Google and MSN for a few key words and key phrases that are related to the web site purpose. Look at the search results. If the web site is at the beginning of the search results, between the first 20-30 results for most of the key words and phrases, and in all three search engines mentioned above, then it probably has a lot of traffic.
The genuine search engines results (not paid PPC, etc) generate the most valuable traffic for the web site owners. Also PR 3 or 4 is very easy to catch and the web site still may have no search traffic at all.

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MBM | Review your host | Know Vista?

By the way,

Alexa is not correct. One can increase the traffic level and trick Alexa's measurement simpli by installing Alexa toolbar and visiting his own web site pages.

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MBM | Review your host | Know Vista?

Thanks mbm I did not know that about Alexa. You would think that it would be an easy fix for them to avoid the manipulation of their results.

It is probably easy to fix, but I think they do not care about that.

It is also very easy to test. Just register a new domain, host one page. Do not add much text. Do not advertize. Do not register in search engines. Install Alexa toolbar and start visiting its only page once or twice per hour. For a wekk or two you will have traffic ranking in Alexa as a very busy web site

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MBM | Review your host | Know Vista?

I agree with mbm. There is not a good resource for estimating traffic and PR can be manipulated.

mbm, thanks for the information you provided in this thread it was very helpful!