The biggest indication that a Trade Bot site is not legit, is that they require a deposit BEFORE you can withdraw your skins. Safe and Legit Trade Bot's NEVER require you to deposit skins, before you can withdraw the ones you want. A reputable Trade Bot transaction will take place within a SINGLE TRADE OFFER. As a general rule of thumb in trading, ensure that all items are present in the trade offer before you accept. Never assume someone will correct their mistake, or allow you to withdraw skins with "credit"
To entice people to use their SCAM Trade Bot, some sites will offer large bonuses (5%+) for putting their site in your profile name, effectivly reducing their commission down to 0%. Some might even offer no commissions. Let's be real here, Trade Bot sites exist to make money. Any site that's offereing 0% commissions is probably looking to make money a different way, by scamming you.
Find a Dragon Lore for $150 or Karambit Doppler for $50? Come across a deal too good to be true? That's because it probably is. Legit Trade Bot sites exist to make money, so they are constantly checking market rates and updating their prices to ensure the arn't losing money from a sudden price fluctuation.
All legit Trade Bot's want to engage you, and keep you coming back to their site so naturally they would have a social media presence. If you come across a site, and their social media links want YOU to post something on YOUR wall about their site, it's probably a scam. Make sure the site you choose has a legitimate social media presence, and engages with their customers.