Dilemma

I setup a 10 gallon aquarium per instuctions from the Petsmart employee. I also checked online and watched some videos to be sure I was given proper instruction. It all seemed to be good except for the adding fish part...no one had the same answer. So, after four days I put in 2 guppies, by the end of the next day the male was dead. Now I've been very diligent about checking the water and the water is fine. So I had a chance to buy three more guppies so I did. I had four...now I have 2. All I see is their gills look a little more then pink but not red...any ideas??? Petsmart is not an option. And do you the community think I should spend more and buy from a Fish and Aquarium store and pay more?

Hope someone reads this.