It doesn't happen all the time so something is triggering it.
https://www.paypal.com/uk/cgi-bin/?cmd=xpt/Customer/popup/PPPolicyForEBayItemHolds-outside"Why might my payments be held?
PayPal will hold payments in transactions where the vast majority of seller fraud occurs. Here are the most common instances in which a payment may be held:
%&$#?@!%&$#?@!%&$#?@!8226;You are new to eBay and sell an item above £50
%&$#?@!%&$#?@!%&$#?@!8226;You have a low feedback score and sell an item above £50
%&$#?@!%&$#?@!%&$#?@!8226;More than 5% of your transactions result in dissatisfied buyers*
%&$#?@!%&$#?@!%&$#?@!8226;You have a low Detailed Seller Rating (DSR)
%&$#?@!%&$#?@!%&$#?@!8226;You have not received a significant amount of Detailed Seller Ratings
%&$#?@!%&$#?@!%&$#?@!8226;You are listing your item in a higher-risk category
PayPal will not hold payments for eBay items if you meet the following criteria:%&$#?@!%&$#?@!%&$#?@!8226;You have been an eBay member for more than 6 months, and
%&$#?@!%&$#?@!%&$#?@!8226;Your total Feedback score is greater than 100, and
%&$#?@!%&$#?@!%&$#?@!8226;Fewer than 5% of your transactions result in dissatisfied buyers*
OR
%&$#?@!%&$#?@!%&$#?@!8226;Your average DSR is greater than 4.5, and
%&$#?@!%&$#?@!%&$#?@!8226;Your have received more than 20 DSRs in the last 12 months
What will happen if my payment is held?
If you receive a payment that is held by PayPal, the amounts held will show as "Pending" in a separate PayPal balance on your account page. You will still have access to all other funds in your PayPal account.
Your funds will immediately be released when one of the following occurs:
%&$#?@!%&$#?@!%&$#?@!8226;The buyer leaves you positive feedback
%&$#?@!%&$#?@!%&$#?@!8226;3 days pass after proof the item was delivered**
%&$#?@!%&$#?@!%&$#?@!8226;21 days pass without a dispute, claim, chargeback, or reversal filed on the transaction"
You can have 100% positive rating but a poor DSR rating. I was excluded from free listing weekends because my DSR was bad, purely because of two parcels that I didn't send immediately because I was ill that day (which I communicated with the buyers who said it was ok). They gave me positive feedback but rated me down with DSR. I tried talking to ebay about it, but all they would do was say I should keep selling on ebay to improve my DSR. Due to the way they work it out I would need to get excellent DSR ratings on 200 more items before I would be allowed to take part in free listing weekends & as that was the only time I would list because of the high fees then I decided to avoid ebay until my DSR ratings timed out.