google for pharmacy review sites, pick ones that include reviews from users and the site owner. if there aren't any bad reviews trash it. Usually a few will get most of the discussion - these are usually the safest bets, but make sure to read the last few weeks worth in case somethings gone wrong.
Try to pick one thats been around at least a year and ships a good variety of drugs but skips commonly abused stuff like sedatives, stimulants, steroids and narcotic pain killers as they are much more likely to be a scam.
India is probably the safe choice. Don't order from anywhere that doesn't disclose their location. Don't order from "brokers".
A large variety of boring medicines in every dose manufactured is almost always going to be legit, trustworthy and not counterfeit. It'll usually come wrapped in foil strips that are verifiably the local licensed pharma manufacturer.
Always pay with a credit card and always expect 2-3-4 week deliveries.