Answer:
they can either, repeat the experiment, or have the experiment, tested several ways, and several times, or have the experiment done in another area with different conditions
They can write a complete description of what they did, and what results they got. Then publish the write-up in a report or magazine that's read all over the world, by other scientists who are working on exactly the same thing. Then all those other scientists can look for mistakes in it, or they can do the same experiment, in the same way or in different ways, and see if they get the same results. Then all of THEM publish THEIR experiments, for everybody ELSE to see, pick apart, and duplicate.
Hey ! This is exactly what real scientists do all the time !
Whaddaya know !
