You are trying to trace a Jacob Schmidt in Berks County during the later 1800s, a common name. You find many possibilities matching his age range—three times in 1870, two times in Civil War records, and four times in marriage records. Which is the real Jacob? One clue may be his occupation.
Most of our ancestors fell into one of two nondescript occupations—farmer or laborer. But many had trades, such as preacher, glass blower, miller wright, doctor, or lawyer. You know that the Jacob you are looking for was a hotel keeper when you found him in the 1880 census. What do the other records say? Farmer? Blacksmith? Are there any that say hotel keeper? The latter may be the correct record.
Keep in mind that many individuals changed occupations. Also, your ancestor may have worked in related fields: e.g. glass blower/glass cutter; carpenter/roofer; seamstress/presser. Many job descriptions are no longer in use. What we call an undertaker today would be a “layer out of the dead” in the past. Google the key words “genealogy” and “old occupations” to find the many lists available online.
Where can you find occupational descriptions in records? To name a few—censuses (look at all those columns of information), marriage license applications, some baptismal records mention parents’ occupations, military (draft registrations, pension requests), immigration records (ship manifests, naturalizations), deeds, and wills.