1) They won't take the offer back, but some company may say that's all they can offer---equivalent to 'no'
2) No, Almost EVERY job offer involves a negotiation, it is common and everybody understands that. If the company REALLY LIKE you, or the position is something they have to fill quickly, at least there will be some kind of room to negotiate.
3) Tell them directly you have another offer, and they give you $$$, but you like this company better than that, if this can match that offer, you'll immediately make decision to take this offer.
Negotiation is quite common, my past company I involved in some interview processes, so I know some American people even negotiate things like the work hours, schedules, PTO, titles, office locations, type of computers they want, etc.
Good luck!