There's no good reason to doubt the accounts that Jesus was crucified once we consider the following:
All mainstream historians hold that Jesus was a real person who really existed and was a controversial preacher in early 1st cent. Roman Judea.
Crucifixion was widely practiced by the Romans against non-citizens during this time period.
All ancient sources we have that mention Jesus talk of the crucifixion as an event that really took place.
Christians cited the specific governor who signed the order, as well as the date, in the Gospels.
Josephus, a historian who wrote about Jews and events in Judea and who was born just 5 years after the crucifixion is thought to have taken place, mentioned Pontius Pilate's order of Jesus' crucifixion. He would have had access to archives and eye-witnesses that could have disproved the account, if such evidence existed.
Pilate's involvement was seen as so important by Christians that it was made into an article of faith in the Niceo-Constantinopolitan creed some 350 years later.
It would have been foolish to make up those details, as they would have been easily falsifiable. While we no longer have written records or eyewitnesses, they certainly would have existed back when Christianity was first spreading.
The untimely execution of one's god, by crucifixion no less, is too profoundly humiliating to be made up.
Christians were widely ridiculed for worshiping a god who let himself be killed.
Some believers (Docetists, Manicheans) were so embarrassed that they held that Jesus was only a spiritual being whose physical body was merely an illusion, or that he swapped places with someone on the cross, but even they didn't attack the historicity of the crucifixion, they just claimed that he only pretended to die on a cross.
No ancient critics of Christianity argued against either Jesus' existence or crucifixion.
If the crucifixion didn't happen, then what happened to Jesus?
If he wasn't executed, surely his followers would have known what happened to him.
If he was executed some other way, why would they make his death even more humiliating?
Early Christianity spread through word of mouth. If he hadn't been crucified, wouldn't conflicting narratives have spread as well?
Taking all these considerations into account, although there is no physical evidence that the crucifixion took place, it's as certain as any other historical fact.
Of course, the resurrection is a different story, as are the specifics of the cruci