Okay, I'm just going to make this a top level post.

[conuly]

If you're referring to the customs of some other people in the past tense, you should stop and ask yourself first "Do these people exist? Do they still do this thing in the present day? How can I find out?" and then go google it. If you're not sure - and if this isn't your custom and your people then you should assume you're not sure - you should see if they have some website in the present day where they tell you what they do today. You should definitely not assume that their quaint old-timey custom is something they did in the past and don't do today, especially if there is a better than even chance that somebody might assume that this is because those people are all gone now.

Of course, on the flipside, if you're assuming people today live like they did in the past, that is also an error and you should look it up. In conclusion, no matter what, look it up.