Bought some glasses from a well known opticians that just don't fit right. There's a 100 day guarantee and so I've chosen new frames. The store have gotten really funny about the swap, despite the guarantee. Anyway, they've said they'll order the new frames but take the lenses out of my existing glasses and try to fit them in. Is this standard practice? Everything I'm reading online says this isn't really a good option because the lenses will be curved/centred etc to fit the frames. Any knowledge on this much appreciated.