It's been a month since I entered the magical world of the miles game. I started very small, only needed to spend 5K for a result of 150,000 miles.
Things I have learned so far:
1) Don't take what people say on flyertalk too seriously. There is so much volume over there that it's really hard to figure out who knows what they're talking about, who's being an idiot funnelling their annual gross income in money orders per month. Do your own research and experiment. I highly suspect that the most successful MSers out there follow the millionaire next door approach of laying low and not bragging (which begs the question, why am I even writing this post?).
2) Regular stores can be a pain in the ass to deal with. I've had a cashier give me a hard time because the back of my card wasn't signed and I didn't have an ID on me. I have had great success in, erm, less savoury parts of town. Cashiers there are less suspicious with the caveat that you can't overplay your hand. I can get away with buying $500 worth at a time but I would look very out of place buying multiple thousands in a neighborhood where a good chunk of people don't even have $1,000 in their names at any given time this year (aside maybe from tax refund time). My white ass sticks out enough already as it is. Obviously if you are to do this, use your best judgement and be safe. I tend to go early in the morning on the weekends when the thugs are still sound asleep.
3) Mixing spend operations with exercise and errands. My SO cooks a lot and inevitably we run out of an item or two. Instead of grabbing my bike and going to the usual grocery store to pick it up, I'll take the scenic route and go to another store in the hood (see paragraph above), adding some extra miles and much needed exercise to my errand. Win-win. I have observed variations in store policies on a regional level as well.
4) These so called "underbanked" products suck. Awful websites, unclear instructions. I can't imagine the life of people who use these products by necessity. I refuse to do business with GreenDot or any other sketchy company that requires me to hand over my SSN. So far so good. Serve is a revolutionary product for those people in the sense that it doesn't suck. Massive kudos to AMEX for having the balls to serve (get it?) that market.
5) Don't be an idiot. Stick to hitting the initial bonus and that's it. Don't load money and withdraw it immediately. Don't argue with people. Stay well within the limits of what would be considered credible with regards to your income. Don't be greedy.