For small micro-transactions, the mutual trust node (MTN) can open the "transaction channel" to perform high-frequency offline transactions. MTN can be formed in two ways: between relatives/friends and between high-reputation peers.
If there are a lot of transactions happening between 2 nodes, it can be inferred that these 2 nodes (the people behind the nodes) would have a frequent social interaction, which means they are socially deep related. As illustrated by figure below, Jenny and Alice are friends, and they often interact through social Apps, such as: chatting through encrypted WeChat, photo sharing, money transfer (Rd Packet or Transfer), leaving comments, etc. For people like Jenny and Alice, who are closely related in real life, with deep social relationships, we define them as "Friends or Relatives Nodes" (FRN). For FRN, the privilege of initializing high-frequency offline transactions is given.
Usually, 2 nodes without prior interactions cannot open payment channels. But for High-Reputation-Nodes, payment channel can be opened even without prior interactions. For High-Reputation-Nodes, since they have a good reputation performance in their own social networks. For small micro- transactions, being a malicious node is economically unfeasible, since the cost of reputation loss is far greater than the possible benefits.