I suppose they don't (less mature believers, anyway).
I guess that's why God tells us to not create appearances that solicit the inaccurate judgements of immature believers. Because they surely are going to judge what it looks like we're doing.
A stab at humor....
Appearances.....you have a concern.....about what people think?
Christ could not be concerned about such things...."The Son of Man came eating and drinking, and you say, ‘Here is a glutton and a drunkard, a friend of tax collectors and sinners.’" Can you imagine the gossiping that would occur if a church congregation went down to a local bar and bought a round and sat and talked to them about Christ and invited them to church....or invited them to a church picnic that included beer. I am thinking Christ would smile, but they would be the talk of the town.
Toasting Christ on the Lord's day...might want to look into that.
Appearances....My concern about appearances is the sin it causes for others that incorrectly judge. Is it a sin to incorrectly judge others and then a sin to gossip about it. Bob and Tina have been "shacking up" for ten years. Part of their church sit in a corner of the church...."Bob and Tina are living in sin." Says John. "Yes I know, their souls be damned!" Says Sally. "And their children were born in sin, born out of wedlock!" Says Peter. "Will their children go to hell as well?" Says Carol.
So Bob and Tina hear about this and are offended and stop going to church and turn away from the Lord. And in fact they go to hell, but not because they were together, but because of the gossip. "but whoever causes one of these little ones who believe in Me to sin, it is better for him that a heavy millstone be hung around his neck, and that he be drowned in the depths of the sea."
Nowhere in the Bible...Old or New Testament is there a requirement for a wedding or vows to be married. Who is going to be held accountable for their souls....the sin of judging....the sin of gossiping....the sin of causing someone to fall away from Christianity and go to hell.
Appearances are important....because you would not want to cause people to go to hell because they are stupid!