horseshoe, as others have said, there is a danger in chasing. Better to just have a general reminder in the package (like on a slip of paper) to say that their feedback is greatly appreciated and you will leave feedback once they leave theirs. But to email you first if there are any problems.
If they don't leave feedback, best to just leave it. From my limited selling experience, I think about 50% leave feedback.
If you have the time, you can go into the buyers' feedback profile to see whether they have left feedback for others. If they left for lots of positives for other sellers but did not do so for yours, there is a risk that it is because they were unhappy in some way but did not want to leave neutral/negative and could not be bothered to ask for a refund/post back.
I know I have done that. Just decided to take it on the chin even though I was not happy with the condition of an item of clothing and did not feel the seller should have even listed the item for sale. When chased for feedback, I explained in an email about how I did not think the amount of bobbling on the fabric corresponded with just a few times' use. But of course the seller will swear black and blue otherwise, as she did. So achieved nothing.
You will get there, horseshoe . I believe eBay rules are changing in May to not give sellers the right to leave negative feedback. That might encourage more buyers to leave feedback, as they do not have to fear retailiatory negative feedback from the seller.