Whether it is considered rude to accept an offer for coffee at someone's house from people you don't know depends on cultural norms and personal preferences. In some cultures or social circles, it may be perfectly acceptable and even seen as polite to accept such an offer, as it shows willingness to engage and connect with others.
However, in other cultures or situations, it might be more appropriate to decline politely if you don't know the people well or are uncomfortable accepting hospitality from strangers. It's essential to use your judgment and consider the context in which the offer is made.
If you feel uneasy about accepting, you can respond with something like, "Thank you for your kind offer, but I'll have to pass this time." This way, you acknowledge their gesture while politely declining.
Ultimately, the most crucial factor is to be respectful and considerate in your response. If you are unsure of the social norms in a particular setting, observing how others respond can be a good way to gauge what is considered appropriate.