Unfortunately due to eBay's acute paranoia with regards to their belief that potential buyers are trying to set up off-eBay deals with the seller if they so much as enquire as to roughly whereabouts in the area in question the seller lives, the only way to request the seller's full address without breaching any of eBay's rules is to commit to purchasing the item first, then contact the seller to ask for the address details in order to be able to collect the item. However, this doesn't always work, as in some cases there are places in the UK that share their name with another city or town elsewhere in the UK. One such example of this is Newport - there are three places of that name in the United Kingdom, one in Wales, one in England and one on the Isle of Wight. However, with no way of being able to ascertain which one it is, if the buyer really wants to find out the address details without breaching any of eBay's rules then he/she has no option but to purchase the item first and if the location ends up being too far away for collection to be possible then the buyer has to request a cancellation of the sale. This not only wastes the buyer's time but also the seller's, as he/she will have to refund the buyer's money and relist the item again, but will be unable to get back PayPal's cut of the sale from the transaction that fell through.
At the end of the day, unless the buyer has included a postcode in the item description so that you can put a trace on the postcode and work out whereabouts the seller is located - which could potentially result in the seller being penalised if eBay were to spot what he/she had done - then you'll either just have to make a decision to either commit to the sale and hope that it's not too far away if you can't ascertain the whereabouts of the item beforehand, or alternatively decide not to bother and see if you can find an identical item being advertised for sale by a seller who is willing to post the item in question.
