Wow! Do these errors happen often in experiments/scientific discoveries? It seems to me that the worse of the two would be the random errors.
Would weighing an item on more than one scale/taking many samples of data from different places help minimize these errors?
Because scientists know these errors exist they try to think ahead of them. When designing experiments you already think about the things you mentioned, such as how many and what type of repetitions to do, the sample size to use, using multiple techniques to double-check values etc.
Designing proper experiments is an art in itself.
I see- that's genius! They must work very hard to perfect the right experiment.