Question

Which could be a negative factor of a barter system?

Both individuals easily agree on the value of their goods.
One person may not want or need what the other person is offering.
Goods can be exchanged without the need for any physical currency.
The process requires money so the two people involved can easily come to an agreement.

Answer 1

One person may not want or need what the other person is offering.

This is the "double coincidence of wants" problem, a key drawback of barter systems that makes trades difficult.