If I see someone with a great bag,or shoes,coat or even smells lovely,and they don't look like they are in a godzilla type temper,I always ask,nod and smile at the bag and say 'oo lovely!' Makes their day!!
Plus if I get it,I love it,its very flattering,I just graciously say 'awww,thank you very much,thats lovely of you to say' if someone has plucked up the courage to ask,and be pleasant,its just manners to be pleasant back I think.
Apart from the time that had me laughing my tits off,a lady came up to me in M+S,said 'oooo,I love your studs,did you get them in here?' when I smiled and said no she said 'I would love a pair that size,did they come from Claires Accessories??'
She must have thought I was totally off my head because I was laughing so much,until I said,'no hun,they are real' she then saw the funny side,apologised and laughed at herself and went off to hunt some down in Claires Accessories!!!