The good Samaritan, who wants to remain anonymous, was queuing behind Ben Lodge when his debit cards were declined at a Lidl supermarket in Redruth, Cornwall.
Mr Lodge was buying flowers, chocolates and steak on Valentine's Day for wife Louise - the bill came to nearly Â£20.
After being traced through a friend and the media, the man declined repayment.
The generous gesture came during Random Acts of Kindness Week and the hashtag #RandomActsOfKindness has been trending on social media in the UK on Friday.
Read more on Valentine's Samaritan and other Cornwall and Devon stories
Mr Lodge, 31, said he left the shop without getting the man's name or phone number.
He said: "I was in such a state of shock at the time that I forgot to ask his name. I was just very thankful and left the shop in surprise."
The recipient of the good deed used social media to tell the story and try to trace him and spoke to BBC Radio Cornwall who helped him track the man down via Facebook.
"He didn't get in touch directly, just through a friend," Mr Lodge said.
"Apparently he is very humble and just wishes we pass the act along some day."
Louise Lodge commented on Facebook: "This is my husband it happened to and we really do wish to thank the man and pay him back.
We will definitely keep the kind hearted gesture going and pay it forward wherever we can."
A man who paid for a stranger's Valentine's gifts has said he does not want the money back but wants him to pass on the act of kindness instead.