As @tressygirl says, if you 'make an offer' payment is taken automatically and you can't choose 'Click and Collect'.
Ebay have said that this will be added later - but don't hold your breath!
Posssible workarounds:
Message the buyer. tell them what you are prepared to offer and see if they will drop their asking price to that figure so you can buy and choose click and collect.
Sellers can disable the requirement for instant payment. If the seller does this, you can make an offer, then get an invoice when it is accepted so you can choose C&C when you pay.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)