i was scammed 500 keys back in 2014 when that was pretty much all i had, now my bp is worth 7000 keys and i have the original hat that was scammed from me a long time ago
if you actually used scrap.tf and didnt use a link he provided your API is compromised and you should reset it
basically that allows them to change trades right before you confirm them
you can learn which effects sell better and a good strat is to offer a little bit better than buy orders and take the first offer that is more than what you paid for it
you advertise and you wait for people to come to you, or hop on a trade server spam chat every 30 seconds for 5 minutes and move to the next trade server