Well buying a lingerie isn't a sin as much as buying a knife would be a sin... It just depends on what she's going to do with it, murdering people would be sinning, and so would buying a lingerie to attract multiple men for selfish reasons... Using the knife to cut meat isn't a sin as God said to kill and eat, so He also made the women for the man and so boosting the attractiveness for her soon to be husband wouldn't be...