I've bought stuff online, from websites in many countries with no problems - with care. Lately I've seen several good looking but certainly fraudulent websites. They appear to be in the US, Canada, and other generally trusted companies. Whois verifies these registrations. Three things characterize them:
1)Prices half or more off for items not widely sold - the expensive mechanical/electronic/optical gear that you rarely see. The reason such fraudulent sites get to your attention is that there aren't many google searches for such items so it's easy to get to the top of the search list. These sites though have extensive lists of low cost - often oddball items - to look good.
2) Contact information is lacking. No mailing/shipping/legal address, no phone number usually no email address either - just a "contact us" box for your message.
3) They show Paypal as an accepted payment method, but if you click on Paypal, nothing happens. If they have a proper Paypal relationship there is no need to enter any billing/shipping address information - Paypal already has it. That click should transfer you to Paypal along with appropriate purchase information. Paypal will verify their legitimacy, your legitimacy and send them the money - if both you and the website are recognized and otherwise pass all Paypal security/screening checks.
So, number 1 says 'be very careful. number 2 says 'no', and number 3 says "No, no, no!'
Be aware though, that if anyone asks you to sign into paypal and send money via paypal, that paypal will let you send money to ANYONE - it's just like you writing a check and putting it in the mail. Be sure you understand the difference between this and 3 above.