Ash-hadu alla ilaha illallah-wa ash-hadu anna Muhammadan abduhu wa rasulullah
"I bear witness that there is no God except Allah and Muhammad (SAW) is His messenger"
There. Once someone recites this, they are Muslim.
Whether they have bumpy road of worship or not is between Allah and the worshiper.. PERIOD.
You can't sit here and say "Oh you did it wrong..you aren't Muslim now" Stop being fucking ridiculous kid..