2nd hand clothes

So consider how fast babies seem to out grow clothes I'd really like to save money by using second hand clothes until I will get more use out of them. This seemed like a great idea until this morning when I met a young mother who had a large number of 0-3 clothes. The car looked like it would fall apart, smelled like smoke, the clothes didn't seem to have a smoke smell, few if any stains and she seemed so hopeful I'd buy them. I felt like it was worth the risk since all outward appearances said she really needed the money and I felt bad. I plan on multiple washes and soaks just to make sure it's all good.

Aside from me being a sucker, I realize there might be some good tricks or tips for buying second hand. Any advice on how to use my money wisely?