This is one of the handful of threads where I've seen a few OTC experiences discussed.

Boy, are they hard to come by - https://old.reddit.com/r/BitcoinMarkets/comments/8ecm6h/otc_what_are_your_experiences/?sort=confidence

If you don't already you should keep an eye on here - https://old.reddit.com/r/BitcoinUK/  as cashing out experiences and bank discussion turn up fairly regularly.

Do you really request whether you want to sell/buy before you get the quote? When you do such a transaction in a financial market you always say that you want both the buy/sell price first so the market maker cant take advatage of you. You tell him later if you want to buy/sell.