Ohhhh dear. Concrete is porous = it stains about as easily as marble. It also has the same level of maintenance as marble = sealing it often (can be as many as 3 times per year). Sealing will prevent stains, but it won't prevent "etching". Etching is from acids (like water, juice, lime mix, alcohol, etc)...while stains are from things like tomatos, red wine, hot sauce, etc.
As a counter top, concrete is considered a "living finish". It will stain, etch and otherwise change/mutate as it ages. As you use concrete, you will create a mottled finish. It is what concrete does. I think the margaritas have started the etching process.
You can slow things down a bit with sealants. These can be DIY or you can pay to have them done. The creator/installer of the concrete counter tops will have what you need to seal them.
Many people will pay to have the first sealing done (they will watch as the sealant is applied) and then they will go ahead and do it from there on in.
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Concrete and chairs
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