Gear Shift Problem....Please Help!

I am having a hard time with my car...I have a manual transmission and I try to put it in reverse, but sometimes it won't go and then i let the car roll back and it seems to go in.
I want to sell the car, but was wondering what the problem might be...and what the cost would be to fix it...
Anyone with an answer???

First of all... ALWAYS post the year make and model of the car.

90% of the cars out there don't have synchronized reverse. There is no problem at all. When you try to engage reverse, the gears don't mesh, so drifting causes them to spin a bit making it possible to engage. Its 100% normal.

agreed.
especially if it is an older car, this is completely normal.
it will only happen about 3 times a month, but it is enough to make you remember it.

if this is the only problem, the car is a-ok