It really depends on what kind of equipment you're talking about buying off your friends.
Straps and wraps, I would not hesitate to buy second hand, BUT straps will depend greatly on condition and whether or not I like the style. Same thing with wraps, but I'm a little more open here.
Belts and shoes can be very individual as size and fit will make a big difference. Again, if you find something that fits and works, then go for it. Knee sleeves probably also fit in this category, but be sure to wash them thoroughly!!
If I missed anything you had more specific questions on, let me know. I've purchased some equipment second-hand, but not much as I tend to be very particular about what I want and how it fits.
I forgot to add that nothing I buy is "custom-made" for me. I buy stuff that weightlifting stores typically stock.