Unless you're desperate for cash, I can't think of any logical reason to use webuyanycar. This organisation don't know a thing about cars other than making a quick buck. If you call them there will be some guy in a polyester suit who simply refers to Glasses Guide, and then promptly drops the price even lower.
Want to sell your car? Give it a decent valet, get it MOT'd, and supply more history than a Mossack Fonseca transaction. Be truthful. Buyers looking for a mint beemer don't want to be disappointed if they've travelled to see your pride and joy.
Good luck with the sale. Personally I'd use newspaper classifieds, or dare I say, Gumtree. If you're a member of a BMW forum, put a shout out.