Arguing that there was no trade between Europe and East Asia in the early Middle Ages because there are no written records of such trade is like arguing that the yeti, an apelike creature supposedly existing in the Himalayas, does not exist because there have been no scientifically confirmed sightings.
Conclusion (implied)
There may have been trade between Europe and East Asia, even though there are no written records
Evidence
Arguing that no trade between Europe and East Asia occurred in the early Middle Ages due to the absence of written records is like arguing the yeti does not exist because there have been no confirmed sightings.
A verifiable sighting of the yeti would prove its existence, but the absence of sightings cannot prove it does not exist.
Evaluate
The argument is presenting an analogy. It compares the lack of written records of trade between Europe and East Asia to the lack of confirmed sightings of the yeti. The argument concludes that just as absence of confirmed yeti sightings doesn't disprove its existence, the absence of written records doesn't disprove the trade.
To counter this argument, we can show that these situations are not truly analogous. In other words, what makes the absence of evidence more indicative of the absence of the phenomenon in one case but not the other?
Goal
Let's find an answer that provides a reason why the absence of written records would be more conclusive evidence against the existence of trade than the absence of sightings would be against the existence of the yeti.