That is hillbilly. Have him cement some uncured rubber roofing to the seam on the inside please. And pull that off.

I've never seen seam tape used on a gutter. The validity of a seam tape is that the non-sticky side is not exposed to water (like covering weather barrier film joints) - here water would get behind it and it will lose it's adhesion.

Gutter connections are waterproofed with gutter seam sealant (caulk!). Joe was actually being nice using the word "hillbilly."

Not a gutter expert. I have seen them made out of many materials: wood, aluminum, copper (gorgeous) and plastic (PVC). Often sections of the latter are joined with connectors with built-in rubber gaskets.

What type of gutters did you request? Gutter caulk can dry out over time.

The guys were recaulking the gutters on our island house. The tube of painter's caulk I had bought the day before disappeared. I searched high and low. No one would fess up to taking it. Years later I figured it out: the worker couldn't read and used the wrong tube!

Joseph is right so do as he said.