I think the trick is to not take these claims seriously and I highly recommend trying the testers, wearing them out and about for a good while, an hour if possible, and then decide if it's the right one for you. Definitely try 2-3 at a time so you can see which matches the best, because if you have just one tester on, you may think it's a close enough match to your skin but you have nothing to compare it to!
Another tip is, it's not always the best idea to test the foundation on your face and try to match the colour to your face. Your face may be darker or lighter than your neck and chest (the neck on many women is usually lighter as it doesn't get as much sun as the face and chest, your chin and jawline can cast a shadow on it), so I think the best thing to do is to match your foundation to your chest. It can easily be applied to the neck too so everything will match.
I do think that we shouldn't kid ourselves about our colouring either. Obviously a tan is nice to look at and it can make us feel better, but in winter especially, we wear tan less and less, so we need to ensure we're not still wearing the same foundation. If you're a pink tone, accept it; if you are quite pale, accept it; if you have very oily or very dry skin, accept it and use these points to help you pick the right foundation. The opposite is also true - if you like to wear false tan occasionally, your normal foundation may not match and you will need to pick a darker, yellow based foundation. There's nothing worse than looking back on your photos of a great night out and your face is pink and pale in comparison to the rest of your body, and the artificial light we often end up applying our makeup in can be deceiving!
So the point is, read the bottle, check it's got ingredients that either won't affect your skin or may even benefit it (foundation for oily skin should be oil-free and non-pore blocking and foundation for dry skin should contain some sort of moisturiser like glycerin), try the testers and be honest to yourself about what shade/tone suits you, wear a good primer underneath that also suits your skin type and will help it last and you can't go too far wrong.
On that note, here are a few drugstore foundations that I've tried recently and what I thought of them:
Bourjois Healthy Mix Foundation - this is a brilliant foundation for oily skin once you have a good primer underneath, it has good coverage but still maintains a little dewiness, which is nice as most foundations for oily skin have a matte finish, it lasts all dry and doesn't really seem to affect my skin one way or another in terms of oiliness or drying my skin out. I'm wearing this foundation on a daily basis at the moment and so far I've no complaints. One downside of the foundation is it only comes in 8 shades and they seem to be mostly yellow based, so some people may miss out.
Rimmel Lasting Finish 25 Hour Foundation - This foundation claims to be extremely long lasting and sweat-proof; I don't know if that's true but it's still a good, long-lasting foundation all the same. It has a slightly more matte finish so I recommend using a silicone-based primer underneath as it will help the foundation to glide on and blend easily. It has high coverage which is good for my blemish-prone skin, but again, it doesn't have a wide range of shades - only 6 in total.
Max Factor Smooth Effect Foundation - This foundation is oil-free and claims to have a smoothing effect, as the name suggests! I'm not sure if this foundation is great for blemish-prone skin, I bought it because it's oil-free so I knew it wouldn't do anything to make my skin worse. It's a fairly light foundation that doesn't have a lot of coverage, but even so, I like it because it has more of a semi-matte finish so wasn't too drying and it was fairly long-lasting. I think it would be good for normal-oily skin types and for people who don't need a lot of coverage, maybe just some evening-out. Of the 3 foundations I mentioned, it's the worst in terms of colour range - it only has 4 and they seem to all be yellow-based/neutral (nothing pink-based at all!)
So apologies for this blog post being long again but foundation really is something I could talk about all day and I've only scratched the surface of all the different types here! I will say that I have bought all the foundations mentioned with my own money, so my reviews are fair and honest. I don't necessarily like to bash products but when a product is generally good I will mention any small downsides, just so anyone reading this can be fully informed if they go to buy anything I mention!
Thanks for reading!