What's a fair price?

I’m not going to be much help either I’m afraid. I used to price my plants depending on what it was my price ranged from 50p to £2. I found I had a lot left or people gave what they either thought it was worth or what they had ( which really pi$$ed me off, because they wouldn’t do that in a shop! And I wasn’t over charging by any stretch of the imagination) . Now I just have a sign that asks for a donation. 9 times out of 10 I get more than I would have asked. Also location & situation makes a difference on pricing. I have to be very aware that most of my customers are impulse buying. Because no one is going to drive a 7 mile dead end road if they not coming for a walk on the beach or go to the cafe. No one is coming just to buy things from my sales barrow.
I get quite a bit of stick from friends telling me I should put my prices up on my homemade items. But people won’t pay shop prices on the side of the road.