The abbreviation "bet shin/ sin tet" on a tombstone almost always means "Be'sayvah Tovah" which translates to "in good old-age", and refers to people who lived to the concept of "old age" at that time, usually well beyond the average life expectancy of the period.
Bet-sin- tet has nothing to do with shem tov (unless it's earlier in the text referring to a person's virtues) or be'sha'a tova, (in a good hour) which to my knowledge is never ever used for someone's death, and is reserved for happier occasions such as births, engagements, bar-mitzvah, weddings...
Hope this helps all those who do such a marvelous job deciphering tombstones...! (and get to it earlier than me!!)
