You make your own luck buying used gear, largely through homework, patience, and pickiness. Get impulsive, impatient, and indiscriminate and you're asking for it. My strategy is get the newest, cleanest, lowest rollage you can afford. Don't sucker for attributes, e.g., "workhorse," "bullet-proof," "can be used to pound nails," etc. They're just machines and they fail with age and working hours, whatever you hear on APUG or elsewhere. Don't buy a holy relic and expect a miracle. Pick a format, features and budget and start shopping. Don't be afraid to take some time and to build up a camera from bits. This can work for you if you're short on scratch. Get a clean body, wait for lens or a film back or WLF. Buy what you need. Always works for me.