so you walk up to the neighbor and say:
I saw some of this type of wall being installed on one of my jobs, not sure it was the same brand or anything though. The installer was telling me the manufacturer of that wall required it to be filled with stone and filled on one side with stone rather than just dirt for drainage and stability and I noticed your installer was using just dirt. Have you taken a look at the installation requirements for your wall? Even with all the arguing we have had, I sure would hate to see you spend that kind of money and it not last because it wasn't installed properly.
are ya ready for a beer? I'll buy the first round.
as to the installer; he is going to do the work and move on. Your neighbor will be there everyday. I would tend to be more concerned that my neighbor thought I cared enough to tip him off than what the installer thinks of me. You apparently have started to build a relationship with the neighbor. This is a chance to show you do have concern for your neighbors.
as to the installer damaging your landscaping and working from your side:
being allowed to work from both sides is a huge benefit so you might offer to allow it IF you have assurances that anything the installer damages gets taken care of. Again, build the relationship.
