Oh OP, I was taught to always knock on two doors by my folks when looking at property. Was a bit mortified in the beginning but soon got over it and discovered if you hit the right chatty neighbor it can be dead useful. Find out about other neighbours, facilities near by I was unaware of, parking issues etc. Also, get a feel of your own new potential neighbours.
Was taught to knock on one directly next door and one a few doors away. Be very open about being interested in the house for sale, ask about the local area, neighbours, kids in the areas/antisocial behavior etc. How they found living in the area etc.
My brother when purchasing a house discovered after some chats with one neighbour that a house he was interested in had flooded the year before due to poorly done pipes. Owner had paid to have it fixed so solicitor and insurance checks hadn't flagged it but nosey neighbour told him all the details.
When myself and OH were house hunting we saw a property but discovered the one directly across the road was being used as an air B&B and short term rental which had been causing some issues (parties, parking conerns etc). Then another property we thought was perfect but when we talked to a neighbor he asked if we had kids. I said no, but I had a niece and nephew who visited regularly and plans for the future. He pulled a face and informed me that the little old man who seemed so nice that we would end up sharing a drive with, he had an adult son who was a convicted pedo and he made regular visits to the house and stayed over increasingly often as the old man's health was declining. Useful information no estate agent or home owner would have revealed.
Always knock on a few neighbors doors. Be polite. Be friendly. Ask some open ended questions. They might be your Neighbours one day soon, or they might tell you something useful.