Shrimp are sensitive, whilst they excrete very little in terms of waste as soon as you add fish this will change and they will be poisoned by ammonia, most shrimp aren't very hardy and odds are they will probably die, best case they suffer for around 4-6 weeks whilst your filter develops the correct bacteria to process ammonia from fish waste.
You should really buy your own test kit, daily or bi daily testing is pretty important when establishing an aquarium and cycling the tank with or without fish, without it your only indication as to tank health is the way the fish behave, usually if they die or become ill it's inductive of poor water quality or incorrect water parameters for species chosen, do you know the pH and gH/kH of your tap supply? This will dictate what you can keep, some fish require soft acidic water, others hard alkaline water.
What is the tank volume? If you plan to add fish before cycling then a test kit is a necessity, be prepared to do large water changes every day/every other day, around 60-80% to bring that ammonia and or nitrite reading down to under 0.25PPM.
You could choose to ignore my advice but I've been keeping fish for over 20 years, fresh/salty you name it I've probably kept it. I'm not trying to boast but my knowledge will be a lot more useful than that of a shop, the thing that exists to make money. 9/10 they have zero interest in the welfare of the animals, unless you go to an independent retailer.
As I stated previously, please read up on fish in and fishless cycling, it is crucial to getting this right and to prevent the needless harm of the animals you are intending to buy, plus the heartache and wanted money from when the inevitable happens...
Also please do your research on the species of shrimp you buy, some species are not suited to general aquaria also and require specialist diets.