Is it real?

When I first started making jewellery I was quite happy to use findings and beads I bought in the local craft shop. There was nothing remarkable, they were fairly cheap and cheerful. I took care to make sure they were free of lead and nickel however, as I wanted to be sure they were safe to wear. As I moved from making for myself, family and friends, I wanted to use better quality findings - my theory was that most of the cost of my finished product was labour. If I used Sterling silver and gemstones I could charge more for the finished product and the labour percentage would be less, hence giving better chance of selling my products.
My local craft shop didn't sell Sterling silver or real gemstones so I started looking round on-line for sources. Most of the time I used reputable dealers and was highly satisfied with the products. Then I saw what I thought was a bargain. It wasn't a silly bargain so it didn't raise questions in my mind and when the items arrived they seemed just fine - the 925 hallmark was quite clear on the tag between chain and clasp. It wasn't until several weeks later that I realised my mistake.
I had been doing a long craft weekend show and wearing a piece of my jewellery, an art pendant on a silver snake chain. The days had been long and damp - typical British summer :). On the last day, I noticed some discolouration on my neck. I took the pendant off and could actually see the copper through the silver plating on the clasp. Fortunately I was still selling previous stock of chains and hadn't used the new ones yet.

Since then I have stuck to reputable dealers, but have also checked anything I buy as sterling silver.
Checking silver is quite straight forward using a kit available quite readily. The kit contains an acid, a tiny ingot of silver and a rubbing stone. All you have to do is rub the item on the stone, add a tiny drop of acid and see the colour change, Compare this to the silver ingot treated in the same way. Sterling silver comes up dark red, higher levels of impurity show from bright red  to green. If  you are still unsure, you can scratch deeper into an unobtrusive area and test again.
Since then I have noticed several scams especially with crystals claiming to be Swarovski. I now buy my Swarovski crystals in factory sealed packs! It is definitely a case of buyer beware.