YoVille will NEVER ask for your password, so please be wary of malicious emails and/or forum posts that request your password, including via web links.
No, there's not the only ones that are still around are not reliable so be careful if you happen to use those. Maybe check ah avg might be your best bet.
Best is to follow auction house average or ask people on here or trade centers, the guides we have now are not very accurate and reliable. You might end up selling it cheaper than its actual worth, so be careful! If you're unsure, always ask for help.