An ill-fitting garment, as pretty as it may be still looks bad if it's not paired with the proper undergarments. If it doesn't fit well don't buy it - it's as simple as that, (as unfortunate as that may be - and as much of a bargain that strappy sequined top might be)
Fortunately, however, engineering has brought to this day and age the possibility of making a relatively ok-fitting garment fit perfectly. Shapewear is gaining commercial momentum as the ultimate must-buy - worthy of an investment higher than that of any other piece of our beloved apparel. It is every stylist's secret, every celeb's on the red carpet and if it isn't already, it's going to be your ultimate wardrobe piece soon. As far as I have myself been in a discerning bra-strap situation - as unfortunate as a mistake that may be - I do not tolerate it - especially when you've already spent so much on an outfit to look your best and then your ruin it completely by letting your bra strap show or simply wearing the wrong kind of bra. A regular bra-fitting is essential to ensure you're buying the right kind of bra. La Senza, for instance, offer this service for free.
Anyway - you'd want to buy most shapewear these days - since it's so pretty and attractive! [I went for a nude theme here but there are of course differently-coloured options.]
Find this on my Polyvore.
I do believe that underwear gives that extra 'oomph' of confidence you might need when out with friends, partying, or even going to an important interview. Confidence is key in every aspect of our lives. Personally, I find that a new pair of panties is enough to set me in the right mood...
I'm ending this post with my favourite Selfridges ad of all time: It stuck on my wall of inspiration in my room.