Was the disturbance in the temple something that "Mark" found embarrassing but felt compelled to tell because believed true (as told by eyewitness(es)) and in order to bring an air of authenticity to his gospel? I think the answer is yes and here are my arguments:
Mk 11:15-16 "And they come to Jerusalem, and Jesus having gone into the temple, began to cast forth those selling and buying in the temple, and the tables of the money-changers and the seats of those selling the doves, he overthrew, and he did not suffer that any might bear a vessel through the temple,"
b) "Mark" forced some damage control about Jesus' actions in the temple:
Mk 11:17 "... he said, "Is it not written: "`My house will be called a house of prayer for all nations,'? But you have made it a `den of robbers.'""
The quote comes from the combination of two different sources (therefore very unlikely to have been spoken by Jesus):
"My house [the temple] will be called a house of prayer for all nations" is part of Isa 56:7. However "den of robbers" is from Jer 7:11 "Has this house, which bears my Name, become a den of robbers to you? ..."
But here, the robbers are not the merchants in the temple; they are Jewish sinners who did horrible deeds (including stealing) outside and then felt "safe" because they would visit the temple afterwards:
Jer 7:9-10 "Will you steal and murder, commit adultery and perjury, burn incense to Baal and follow other gods you have not known, and then come and stand before me in this house, which bears my Name, and say, "We are safe"--safe to do all these detestable things? [no mention here of merchant's activities in the temple! No mention in the "Jesus' disturbance" of Jewish criminals/sinners visiting the holy place for atonement!]"
c) Soon after the narration of the ruckus, "Mark" wrote "And the scribes and chief priests heard it and sought how they might destroy Him; for they feared Him, because all the people were astonished at His teaching." (11:18).
"Mark" avoided to say these scribes and chief priests began to look for way to have Jesus killed because of the "disturbance".
d) Allegedly one day later: "Then they came again to Jerusalem. And as He was walking in the temple, the chief priests, the scribes, and the elders came to Him. And they said to Him, “By what authority are You doing these things? And who gave You this authority to do these things?” (11:27-28)
The doings (likely meaning the disturbance) are not treated by "Mark" as an offence but just as a non-punishable incident.
e) Later "And they sought to lay hands on Him, but feared the multitude, for they knew He had spoken the parable [of the tenants] against them. So they left Him and went away." (12:12)
Again no mention of the ruckus. The reason for the chief priests wanting to arrest Jesus is again because of the teaching, not the disturbance.
f) After the arrest, during the alleged interrogation by the chief priests and the so-called trial by Pilate, again the disturbance is never mentioned as a cause for punishing Jesus.
All of the above indicates the ruckus in the temple by Jesus was not an invention by "Mark", but rather something heard from eyewitness(es), which he felt compelled to put in his gospel (for sake of bringing an air of authenticity), reducing it as just an incident with little or no consequences. Why?
Most likely "Mark" downplayed the "disturbance" in order for it not to look as one of the reason for Jesus' arrest (& crucifixion). The other probable cause for Jesus' demise, the fact some Jews then believed him to become "King of the Jews", is also treated the same way (see here
Surely, "Mark" did not want Jesus thought to be crucified because he was a trouble maker with (believed by some Jews) a royal destiny (therefore a rebel from the Roman standpoint). Instead, what Jesus says, not what he did & was believed to become, is the cause of his arrest.