We help assess tech startups at my current company, and we do VC-style investment. These have very low probability of success, and the key is to look for something that can offer 10x to 100x return in the case of success. Confidence in the management is key... you have to use your gut to detect bullshit, flakiness, or lack of motivation.
It's more of an art than a science, so it has a lot to do with how you read people and your street smarts. Are they a con artist? Are they a bullshitter? Are they a drug addict? A slick talker with no clue what they're doing? A disorganized person who lacks follow-through? Someone who is likely to flee the country and take your money? (This does happen)
Simply doubling or tripling your money isn't worth the VC investment. Make sure the 10-fold return is possible, at least!
Talk to the people... a lot. Research and understand their field, and ask them lots of detailed questions. Make sure their strategy makes sense. Look them directly in the eyes. Our CEO has a rule of thumb... if you detect anything that's off, or makes your gut uneasy, then you bail ... there is no room for doubt here.
Don't misinterpret this as values/morality, but I have zero tolerance for drug use. Drug use is extremely common in society and someone under the influence can not, in my opinion, make the sharp decisions needed to achieve success. Or their drug habits get the better of them and before you know it, your investment is funding some guy's cocaine-fuelled party binge. This is just my opinion and my advice, DO NOT lend money to drug addicts. (You mention the fashion industry, so I'd be careful there)