There may be some sites where you can find a legitimate astrologer. But there are also those which are only there to scam you.
I fell for such a trap a long time ago: I used a site's free reading, and received basically the same info you get from an automated natal chart combined with daily horoscope listings in the newspaper.
But the site had insisted it would only email the 'astrology reading' after their psychics had done the work, so I had (quite foolishly) entered my email. Then came the psychic pspam (sorry, I had to). The original site was mailing daily or more with "Your future depends on this! Purchase your in-depth reading or it could mean tragedy!"
Unsubbing meant nothing more than unsolicited emails from other supposed psuchics and astrologers, all asking to do paid readings.
So to put it all into a nutshell: Be very careful.