Just buying something on ebay, pickup only, couple of grand purchase price. Highly likely a legitimate sale but with imagination, the mafia could be involved. So whereas I not too concerned, it wouldn't hurt to pay in a way that minimises the chance of not coming home with the goods or my money (or simply not coming home).
I know it sounds ridiculous and I'll laugh after, but it's probably a good general thing to know - how best to pay when goods are being picked up?
In this case, they do accept PayPal, but my experience with PayPal has been they don't protect the buyer unless they can get money out of the seller.
Carrying cash is fine, just don't do anything silly. Meet in a public place, and if they ask you to meet at their house (item too large to take in public) then leave the money locked in the car until you've sighted the item.
Honestly no one is going to rumble you for cash, it's too risky for them as you're an unknown. What if you know Kung fu? Or have a knife?
And obviously don't go carrying heaps of cash on you for days on end, that's just tempting fate.
If you're really worried you can see if they'll accept a bank cheque, but I think you're probably really over thinking things.
Take precautions and watch out for red flags, but otherwise it'll be fine.