I have taken a deposit on a mare I am selling. Lady who put deposite has scheduled a pick up and has rescheduled three times. Going on two weeks. Keeps having work excuses and have tried to be understanding. But have turned away multiple buying because of deposit. What do I tell lady, what do I do. I am feeding and loosing potential buying waiting. But took deposit and feel stuck.  Never been in situation. 

If there is no contract stating you will hold for multiple weeks, then require her to pay for board/feed per day, or the deposit is given back and you sell to the next person. Holding a horse for a few days-a week is understandable, but multiple weeks isn't unless she is paying for the board and feed. 

If there wasn't a time limit on how long the deposit would hold the horse you're kind of stuck. 
most deposits are non refundable but if you didn't have this and the p/u date in writing ...that's another problem. 
I would reach out to her, pin her down on a pick up date and warn her that you're going to take the deposit and sell the horse to someone else if she doesn't execute. 
If you want to do Deposits they need to be big enough that people don't want to throw them away easily.

Yes I have always had a no refund policy on deposits.  I am trying to be understanding and patient, cause stuff happens. But she also did this first time I put mare up for sale but made no deposit, I have her a week no show so back up for sale, she reached out and said I want her and put a deposit to hold. And said I'll be there Monday. She gave a 1/4 deposit down so thought she was serious. Don't wanna be a a$$ but don't wanna keep lingering it out eithwr

Keep your horse. This girl doesn't sound to responsible to me. When I was breeding, I had the attitude of, I don't have to sell a horse to you. I had a responsibility to the horse I was selling. To find the best home possible. I would count the days the horse has been with you & deduct board & feed & say, sorry, snooze you loose to the girl & if there is any money left, be the good person " regardless of how much you dislike her right now & I don't blaim you" & send the remainder back. 

Does the buyer live far from you?  People nowadays are so dang shady, I hate selling pretty much anything. Got a run around on some old hay I wanted out of the barn, I was selling cheap. If you're anything like me, I try to give most people the benefit of the doubt, be kind, patient and understanding... usually seems like we end up getting hosed! I'd give her till the weekend to pick up the horse and I'd also tell her that if she ends up backing out of the sale all together, the deposit will go towards the horses feed and care for the time she couldn't pick up. Feed isn't cheap these days and you've turned away multiple buyers. You'd think it'd be common courtesy. It's non existent these days. 

Call her & tell her she has 5 days to pick her up if she doesn't you are going to start charging her $15 a day care. She has 15 days to pick her up or she forfeits her deposit & you are putting the horse back up for sale. That gives her a little warning time & she shold be able to get her in that amount of time