I've had many constituents approach my office whose family members have applied for visas. When they are rejected, the letter is usually very brief and doesn't really explain much. It's a very generic answer that they get, usually along the lines that immigration officials don't feel that they're going to return to their country. Sometimes it's because they're single; basically, it implies that they might do a marriage of convenience at the time.
I'd like to know what objective criteria visa officers are using when arriving at those decisions, because I'm concerned that there may be potential for arbitrary and inconsistent judgements happening.