I've had my PayPal Credit account open for over a year, and have NEVER had issues. Not sure why all these bad reviews; perhaps it's due to people not taking the time to read policies? They have never randomly initiated hard pulls like one reviewer stated. I think this is because "Bill Me Later" has changed since this reviewer applied (they did say it was over 5 years ago) and I've pored over my policy documents with a fine-toothed comb and there is nothing in there stating they will periodically check credit scores. My APR has never wavered. As for them taking payments immediately from a bank account but then posting in 21 days as another reviewer said, well, this has never happened to me either. My payments post within 3-5 days. Can't speak about their customer service because, surprise! I have had no reason to call them!
I will admit that Paypal's checkout process used to be slightly confusing, and can see why some people were inadvertently applying for the Paypal Credit line when they didn't want to. But this can be avoided by carefully reading before clicking. Read. It will help avoid surprises later. It's not that hard.
The one thing I thought weird was when they extended my credit without my requesting it. This happened on my one year anniversary of having my account open. I logged in and found I had an extra $300 of credit. I found it odd they did this without me initiating it, and was ready to go on the war path if my credit score got dinged. Good news is there was never a hard pull, so my score never wavered.
I like my account and have never had problems, so reading about mostly negative reviews is perplexing. Maybe I have yet to experience all these awful things?! Perhaps. But so far, so good.