If you don't mind me saying, I think you maybe need to think about what you could have done more, rather than just going somewhere else straight away.
For example, on the first day, I would not have left my children there without talking to the manager and their key-workers, finding out how they would be comforted if required and what strategies they use, asking them to ring you later on for an update, or you ringing them.
They should have been proactive with an introduction etc, but preschools are very busy places, so you should have made sure this happens.
If you take this at face value, what has actually happened here? He had an accident and someone asked him to wait while they got some fresh clothes, but I think that he wandered off. Clearly the staff priority was getting the clothes ASAP and i don't think that is so bad. The other member of staff walked right past him to some and get the door - but why not if someone else was dealing with that situation already.
The chocolate bribe is a bad one, but perhaps you could look at it as a clumsy way to let a child know that if they can behave well they will be rewarded. You can work with them and explain that a better way of dealling with this is ....... Some parents wouldn't have a problem with that and they don't know you or your child so you have to tell them.
And the crying after you left is very natural - did you talk to them about whether to call you after half an hour if he hadn't settled or tell them just to deal with it. Again i think it comes down to you managing them as it were.
I completely sympathise with you, I really do, and I remember my own children having all sorts of problems at their preschool and that awful feeling of whether i was doing the right thing sending them there.
I am just trying to say that whether you leave them there or go somewhere else I think you need to take more control with the staff and making sure you know all about them and how they do things, and telling them about how you like to do things. And if you want to stay for a bit until you are happy with how things are working, bloody well do so - if they say no, then get them out pronto.