I have been creating my own handmade and craft items for many many years now, and I also buy them (can't resist!), but I still get caught out occasionally...so to refresh my own memory and help others, here are some questions you really should ask...
1. Painted Items - How durable is the paint? Can you wash it? What do you intend using it for - if you are buying a handpainted mug or plate for example, you will want to know if it will withstand heat, washing - can you put it in a dishwasher? ...Or microwave, or oven etc.! Has the paint been approved for use with food?
2. Are you buying for a child? Are there any small parts, choking hazards, fluffy bits that might come off etc.? Consider the age of the child carefully - expecially younger children - how embarrassing if your carefully chosen gift is put in a cupboard never to be seen again, by their protective parents...
3. Jewellery - Especially bracelets on elastic plastic thread...how thick is the thread. Most of this type of thread (looks clear in colour) will eventually give way, depending on the thickness and amount of wear it gets. If the thread is very thin, it will break much quicker - I have had some that lasted mere days! It goes like a cheesestring, with bits peeling off and then breaks.
4. Gold coloured jewellery...I bought a lovely bracelet last summer...beautiful lampwork beads on a charm bracelet, cost me £25 at a school fete, from a well known and respectable local craftsperson. Turned my arm black in two hours! If you are paying a lot, you deserve metal of a decent quality - ok, you are never going to get real gold for that price...lol...but silver plate, rhodium or chrome will stand the test of time. Even the elastic is better!
5. Wooden items - check things like the method of sticking it together, make sure there are no pins or tacks protruding, check it for robustness, and be very careful with childrens toys...
6. Fabric and knitted items - Will it wash!
With any item bought from the person who has made it, be aware that 'handmade' does NOT equate with 'cheap'...mass produced it is not! The seller will want a reasonable price for their efforts. Lovely handmade cards are expensive to produce, labour intensive - but you are getting a unique product. You have to expect to pay for that.
One last thing - but absolutely vital.
GET THE CONTACT DETAILS FOR THE SELLER!!!
Obviously not a problem on eBay, but out there in the real world at craft fairs and school fetes, remember to ask for a business card!