I ran an ad campaign which didn't really gave much result. (I got a lot better from Google Adwords for the same amount).
I had decided to cancel it but I wanted to use up my ad credits first -BUT- of course Yahoo auto-refilled-them, charging my credit card without me knowing. I didn't know about auto refill at that time since I was new with Yahoo.
When I found out about auto-refill I tried to find when they do that and it's not so easy I can tell you. From the limited information you get from Yahoo's site, I again set the campaign to cease before I would hit the limit for the non-voluntary auto-refill.
I was sad to see that information was not correct. They auto-refilled it prior to that.
I searched this forum and someone said there is a way in the admin panel of Search marketing where you yourself can turn auto-refill off. I can tell you there is NOT, atleast not in my interface and that is confirmed by Yahoo since I mailed them and asked if there was an off button for autorefill.
What you can do is mail them and ask them to turn it off, so I did!
I had expected several days for my remaining ad credits to get to zero with my current budget but whooops... 1 day later I got a mail saying my balance had reached zero with unusually few clicks! Much fewer than I had expected from that amount of ad credits left. I had not changed anything with the campaign except mailing them to turn off autorefill.
So, I was suspicious and logged in and saw the balance which was 200 usd left!!!!!!!!
I mailed Yahoo again and said "you say in the mail my balance reached zero, amazingly fast after I cancelled autorefill. On my screen there is 200 left."
On their reply they said something about their system is lagging and failing sometimes and that my ad credit actually was zero and also (Of course) detailed instructions on how to refill.