Let us take a look at how much the Trading Companies are asking for people who want their copies of said card:
Top Cut wants 63 boosters and it has an asterisk by the cost, so they won't accept the more common boosters. Their current trade ratios for boosters looks like this:
0.1:1 Packs: HeartGold & SoulSilver, Unleashed, Undaunted, Triumphant, Call of Legends
0.67:1 Packs: Black and White (Please note this discount may not apply to certain '*' rated cards)
0.8:1 Packs: Noble Victories (Please note this discount may not apply to certain '*' rated cards)
1:1 Packs: Boundaries Crossed, Dark Explorers, Dragon Vault, Dewford League Bundle Pack, Mauville League Bundle Pack, Next Destinies, Plasma Freeze, Plasma Blast
1.25:1 Packs: Dragons Exalted, Plasma Storm, Rustboro League Bundle Pack, Primal Clash (Primal Clash packs are 1.5:1 for '*' rated cards)
1.5:1 Packs: Furious Fists, Phantom Forces (These packs are not accepted for '*' rated cards)
2:1 Packs: Emerging Powers, Flashfire, Legendary Treasures, XY (These packs are not accepted for '*' rated cards with the exception of Emerging Powers)
So if whoever made you that offer instead had to trade their Primal Clash boosters to Top Cut, they would need to up the offer to (63 * 1.5=) 94.5 boosters!
I was gonna check other places, but that is a pretty big difference and Top Cut hasn't ever struck me as being that far off. As such, I'd hold out for at least a little bit higher of an offer. You aren't going to be able to ask as much as Top Cut but unless I blew my math you can probably hold out for another 10 or even 20 packs and have the other party walking away happy.
Anyone else want to weigh in? I'm honestly still learning this myself. ^^' I know if I were someone trying to find a good deal, I would be only offering 50 or so Primal Clash boosters and slowly raising until I got to the 70 or 80 booster pack range... but that might not be right either. @hypnotoxic probably could give a better answer.