It would be best to read the sites we listed earlier so you understand the problems more thoroughly, but anyway here are the basics you will need to do to keep him from getting worse.
Proper lighting: UVB and UVA emitting bulbs. If you are using a fluorescent tube light such as ReptiSun 5.0 you will need a regular heat basking spot too. Any regular light bulb will do. To determine what wattage you will need measure the temperature of the basking spot branch and adjust the bulb power to maintain the temp you want. If you choose one of the heat and UV emitting incandescent bulbs (PowerSun, Active UVHeat, Dragonlights, mercury vapor, etc) someone else on the list will have to give you opinions...I don't use them. They put out a lot of heat, so placing them over the cage takes more care to avoid burns. He should get exposure to UV light for at least 12 hours every day. Save worry by putting your lights on lamp timers so you won't have to remember to turn them on or off.
When the weather/temp is right get your cham outdoors to bask in "real" sunlight for several hours every week. This will really help and you will notice your cham is more active and generally healthier.
Proper diet: Gutload your insects for 2-3 days before feeding. There are recipes for very complete gutloads on www.adcham.com, but you can also create your own using fresh dark leafy greens and veggies, fresh citrus fruit, vitamin fortified cereal such as Total, bee pollen, etc. Many commercial cricket feeds are very poor. I do not use catfood as it is very high in some complex proteins that are hard for chams to digest. I have mixed in some good quality fish food too, but don't use a lot of it and most general pet shop fish food isn't great.
Dusting: RepCal or Mineral with D3 are used by many of us for calcium for chams kept primarily indoors. You can overdose it and it is only to round out a good insect gutload. Healthy adult chams need it about once a week. Vitamin dust such as Herptivite can be used about 2 times a month.
Your cham may live very well if you correct his problems with good care. That is the most important thing.
As for reporting a poor pet shop it will depend on where you are. Most cities have a specific agency (might be county animal control, agricultural inspectors, or police inspector) who regulates pet shops. Call your city offices and ask who to report a bad shop to. I'd also suggest you print out the correct caresheets from the websites we listed as "proof" that the info the shop gave you was bad. Otherwise it is your word against theirs. You will need to help the agency document that the pet shop was careless or ignorant of proper care for animals they sell. Also, check the health and info they give for other animals for sale. If they are not housed correctly, are dirty or unhealthy it will help make the case for the shop being fined or "punished" in some way. A lot of times they are just as ignorant as the buyers...and will need to be convinced that they have an obligation to provide the RIGHT care info so their animals don't suffer.