you shouldn't really have a problem if you've only met once and get married , as long as you have good evidence spread over months..
but of course the more times you have met the better
not many people are refused a fiancée or spouse visa if you send the evidence your asked for (well over 90% get their visa)
those that might struggle to show their relationship is genuine are those who have met someone on holiday, get married or engaged then apply for a visa straight away.
but like i said you shouldn't have a problem if you've evidence of a genuine relationship..