Examining classical works by authors not well known; missing data etc on their life. Can the details be considered reliable or not?

Ancient passages provide the world today with a description and a sense of feeling of what the world looked like at the time. From descriptions of the land, events taking place such as wars, to the epic tales of some of the heroes of the day, these ancient passages give us valuable information from that time period. It can be said that our world today is simply a newer world from that of the ancient …

…Tacitus is talking about two individuals named Titus Vinius and Cornelius Laco and he openly shows his attitudes towards them when he says "one the most worthless, the other the most spiritless of mankind..." It is clear that Tacitus did not have a positive opinion of these two and states this in his passage. This evidence cannot be said to be totally reliable since Tacitus may just be stating his own opinion of the two.