what are the two possiable problems with drawing a line of best fit by hand??

Answer 1

Will not be as accurate as it will be harder to draw the line.

Also you may draw it in the worng place as you may interpret it in a different way or interpret it so that it suits the way you want it to be.

Answer 2

1. It could be incorrect (e.g. y = 2.55x + 3.12 instead of y = 2.55x + 3.28)
2. The slope could be skewed (e.g. y = 2.42x + 3.28 instead of y = 2.55x + 3.28)

Granted, those are basic examples, but you get my point.