First you should make sure what type of smoker your friend is and what his/her lung capacity is. A four-foot bong isn't going to be very practical for someone who can only hold their breath for a few seconds (these people do exist). Also, be sure they want a bong. Many smoker friends of mine would not like a bong and would greatly prefer $50-100 in rolling papers, etc. There are many high-end brand name bongs that will offer you consistent good quality. These are also the ones the headshop employee will probably recommend to you because they have a high ROI for the store. This is your easiest and most expensive option. Popular brands include Roor, Illadelph, and Zong. Assuming you're buying glass, thickness is definitely an issue - your friend definitely isn't going to gain any coordination when around this puppy. Not all glass-like materials are actually glass, so give the bong a light flick of the finger and be sure to ask what it's made of. Also regarding materials, the highest-quality glass bongs will be what's called "glass-on-glass," meaning the slide does not require a rubber gasket and instead is fitted air-tight into the main bong chamber. The purpose of a bong is to cool smoke. So, extras like a diffuser, extra percolator, and ice catcher, the latter being the cheapest and IMO best addition to the bong, are worthwhile but luxurious additions. Google or a headshop employee will easily show you what exactly these features do. If you're a nonsmoker then you're probably thinking headshop employees are like, used car salespeople or something. Not true, generally. They're usually stoned, very friendly, and very willing to help someone in your situation. Find some good shops in your area and start a conversation.