Is is frowned on to contact other members to get more feedback on a particular provider?  Or is that business as usual?

When I get an inquiry, I usually make a reply, because I've made inquiries myself. In order to clarify something in a review, or to ask specific questions that may not have been addressed in the review, I will reach out from time to time.

I'm always respectful in asking first if I can make an inquiry, as not everyone is amenable to discussion with someone they may not know. Having reviews and some board presence helps going both ways in communications.

...many replies until you've established yourself with more reviews/white lists and/or a posting history.

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I don't get a whole lot of unsolicited e-mails, but when I do I generally respond unless the e-mail was inappropriate.

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I feel much the same as the guys above. I'll usually help out a fellow hobbyest if I can, and lots of guys have provided me with info when I asked.  

Only exceptions are that I won't respond to an alias, or to crude or vulgar remarks.