Personally I would not pay that amount for the coins but I must admit there are very few around in that grade and getting any sort of decent grade shillings or sixpences and half-crowns is a right struggle , go with your heart .
You might see a flying orange flying man-baby in london complaining about us being late for the third world war (well they were late for the first two weren't they?)
A lot of the fakes are described as silver (they are not) they are base metal but it could be another way of making it difficult to these sellers by reporting them
Interesting coin the 5 shilling piece the old age pension was introduced in about 1905 or 6 and all over seventies got five shillings (A crown) to live on .
Over the years inflation increased its value to approx. where the old age pension is now £200 .Almost a eight hundred percent increase
Funny enough £200 was about the amount I paid for the coin about a year ago , it might fetch £250 now if i was lucky.
Lots of strange coincidences there though.
Looks like a real winner now , I would try it sometime with a suitable coin I am sure you have at least doubled the coins value , its not worth a fortune but there again who wants to experiment with really valueable coins.