You had it advertised at a "delivered" price which most of us would assume is the final price just like it is on something like eBay or amazon, to then spring fee's on top is a dick move without having a line in the advert stating fee's are to be added if choosing PP payment method, fee's are small on a £30 item but not so much on a £300 item. All it would take is 30 seconds of your time to avoid situations like this, not really hard is it?
Paypal policies does state:
No surcharges
You agree that you will not impose a surcharge or any other fee for accepting PayPal as a payment method. You may charge a handling fee in connection with the sale of goods or services as long as the handling fee does not operate as a surcharge and is not higher than the handling fee you charge for non-PayPal transactions.
TM and WE mags will fit and feed fine, i use a mix of TM, HFC and a WE extended mag in my 15 year old m9 and never have issues 👍