1st Come 1st Serve (or reserved) Doesn't Really Apply

This is absurd....and not the first time to happen to me.

I shop online through the used items website on the University of Jyv�skyl� and often find great deals.  I also often set up appointments to look at something, 99% of the time buy it and am quite the happy customer.  HOWEVER I am upset this morning big time.

I found a potential children's bed a day ago and contacted the seller, who lives nearby and arranged to meet her at her home to look at this children's bed (as it's no longer on the store website - older model and she didn't have any photos).  We agreed to meet at her place at 11am, which was fine by me, until Tim told me he had to get to the university around that time.

So I emailed her again and notified her that I can be there for 6pm - ASSUMING that since I appeared to be the first person to contact her about the bed - she would RESERVE IT FOR ME.
Well, I got an email this morning before 9am stating she sold it already.

Thanks a lot Maarit.

What is it with the whole "set a time but sell it to someone else first"?!?!  There's no point in sending her a nasty email because the item is sold already.  So I shall complain here.
Had you said something along the lines like "If you cannot meet at 11 for whatever reason, then I have to sell it to the next person who offers to buy it" - then that'd be fine.

Is there some Finnish un-said law I don't know about when it comes to buying and selling things second-hand?!?!?!

And Maarit...have the decency to not do this to the next person you're selling to and remove your ad.  I wouldn't want other people to be disappointed like I am!