I stopped to use regular bitcoin and crypto exchangers long time ago: being myself a bitcoin millionaire, they are simply not practical. OTC, is in my opinion the best way to buy and sell large amounts of crypto.
I will provide here a list of crypto OTC brokers/ OTC Exchangers /OTC Desks so, if you are dealing with large amounts, you can try to
The fees are usually very low.
You will, most of the time, need at least 500000 USD to start a deal with them.
I'll try to maintain this list updated.
www.kraken.com Kraken OTC ServicesComment: One of the most used. Beware of their KYC requests, it can takes a lot of time and a lot of documents and source of funds needed. Not the most cheap, though, and some bad reviews online.
www.itbit.com ItBitComment: One of the oldest OTC broker. Fast bank wires. Kyc a bit easier than Kraken, but still... I don't use them anymore so my review is not 100% updated.
www.cashgold.me CashGoldComment: One of the oldest (alive since 2013) bitcoin exchanger. They are easy to deal with. Note that they have minimum requirements, concerning funds, higher than Kraken, so don't approach them with your 100K bucks.
I'll finish the list soon.