Unfortunatley seems to be a trend, tried one in Kilmarnock a while back that I was unsure but did like the look of. In the end it would have been £200 for a half hour. Personally the only extra I find acceptable really is anal. With the rest either offer it or don't. If you have to pay extra to get it, probably means she'd rather not provide that service and it'll be shite anyway.
Maybe make exceptions for those well reviewed on here where that service is well reviewed.
