A manager of a Mandurah grocery store has spoken out about his concerns seniors in Mandurah are falling for a phone scam in which criminals pretending to be from Centrelink ask them to buy hundreds of dollars worth of iTunes cards to avoid losing their pensions.

Ben Williams, from Woolworth's Mandurah foreshore store, said two older people had each tried to buy $400 worth of the vouchers to mail to scammers on Monday.

Ben Williams, from Woolworths in Mandurah, is worried about seniors falling for online phone scams. Credit:Nathan Hondros

But luckily he managed to convince both to go across the road to Centrelink before parting with their hard-earned cash.

"These people do make it sound very legitimate and they give you a reference number and a number to call," Mr Williams said.