If you're worried about your exchange double-crossing you in that manner, you probably shouldn't be dealing with that particular exchange in the first place.
The exchange happens to be Coinbase(GDax). Whenever I have had fiat transferred back to my bank, the transaction is clearly marked as being from Coinbase. I'm probably being paranoid. However, banks have to be diligent about "suspicious" activity. All it would take is for some bank employee doing a random audit to see that I have had a cash transfer(s) from Coinbase, find out Coinbase=BTC, and then close my account for "suspicious activity."
What exchanges pay you with paypal money? Also I wouldn't trust Paypal with any larger sums. I once sold most of my vinyl records in a short period and paypal froze my account. I had to prove this and that to be able to be able to use my funds again. It took months and I was really broke (that's why I sold my vinyls) so I'm still quite pissed.
Coinbase allows you to sell your BTC and then they transfer the fiat to Paypal. Almost instantly. They charge a fee though. Since Coinbase went into an agreement with Paypal, I'm sure the funds won't be marked as suspicious. The sums that I have transferred to Paypal so far, (Only have done it twice) is only 3 figures each.