+1 to everybody who's essentially said "why?".
There is NO reason in this day in age to use cashier's cheques. Paypal is great for BOTH parties (can still be scammed though, read the seller protection policy EXTREMELY carefully). If you're worried about the big bad internet having your CC details, do a bank transfer (risk is on the buyer's end, seeing as they're the one unwilling to do it the sensible way!). Money wire etc. works too, again, with some hassle/risk which should be assumed by the buyer for being difficult in the first place.
IF they INSIST that they send a cashier's cheque (because they're just way, way out of touch, or something crazy like that), then the "premium" they pay for that service is that they wait till it's cashed, and it's been verified good. That could easily take two months, depending on some banks' reversal policies. But - if they want the gear, and are insisting on being difficult - that's the consequence.
They can't say you weren't flexible