The biggest mortgage lenders in the United States are firms like Lending Tree, Quicken Loans, Wells Fargo, Bank of America, etc. They have many employees to manage accounts, keep efficient records, maybe even record customer conversations.
Owner carry is a little different.
I have often referred to owner carry as the Wild, Wild West. Remember, it is two people agreeing to terms on a real estate sale. And, typically, after that transaction closes, the two parties are now left alone to fend for themselves. Because of this, all kind of stuff can happen, and some of it is bad. I have had several note purchases fall apart because the seller is suing the buyer or the buyer is suing the seller and I was not told this up front. Sad for the parties and sad for me.
My experience is that these situations are primarily “he said, she said”. One of the parties agreed to do something, the other party feels that “something” was not done, arguments follow, anger builds, payments stop, and a lawsuit ensues.
If you carry a note, and especially if you decide NOT to hire a third party servicing company, I strongly urge you to take notes on every encounter you have with your buyer. And, after that encounter, either phone or email your buyer to get his agreement that your recollection of what happened is correct. Your buyer should respect you for taking this approach. And hopefully, any potential future problem can be avoided by a simple reference to your notes, and you and your buyer can continue to benefit from the transaction you both willingly entered.