The tone of this thread gives the impression that you are seriously not a happy chappy
If you have an agreed timeframe between yourselves then that's the matter resolved, pending the actual refund
With reference to the delivery contract being between him & RM and not you, I partly referenced this with my post about the level of compensation.
This is not in reference to the specifics of this case, but in general towards private sales on the forums - sometimes buyer & seller will negotiate specific postage options, perhaps because the buyer does not want one carrier or prefers another,but often due to cost
Sometimes you can send a parcel of x size/weight for less, or standard post has a compensation limit
In such a situation if it goes missing or gets damaged then compensation becomes a problem - not enough insurance means someone loses out. By default it should be the seller, but if the buyer wanted to cut the cost to a cheaper service then they have contributed to the loss in compensation
For PayPal as a payment method, it's again not compulsory, however for the payment of £450 this would have cost £16.05 in fees
Rather not spend an extra £16 on fees, however to lose £450 is a different matter
It is going to end up ok, but you may feel better at the moment if you had that protection to reassure you that it will come back to you
People have bought without PayPal for a long time, but in addition to bank transfer & wire transfer which can leave you easily subject to scam there have long been escrow services. That's the service PayPal provides
