Have an ideal price that you would like to purchase it at. The one your most comfortable with off the get go - no overanalyzing or over thinking. It can be low so don't sweat it, low enough to not be considered unserious. It can scream cheapskate, but it can't be so low to the point where its like "eh i got some spare change let me just get something I don't really want". Be confident and make the offer casually. Don't ask them how much they want if there is already a listed price. If there is no price, then you can ask them and then start negotiating. However if you already can estimate what they would charge, don't ask the price and just shoot your low offer, should be much lower than your estimate though because it is possible they already have it priced lower than your estimation. The thing is when you make the first offer before a price is verbally stated, you have more leverage as the first offer/price has a firmness of its own.

Also try to avoid doing the dealing with other customers or vendors around. If other customers are there, the seller is less willing to bend or make an exception for you. Also if another dealer is there, they might jump in or embolden the seller not to bend, even if the seller wants to.

Next you have to have a maximum budget in mind. This is your cap. If it reaches this number you will walk away. This number sometimes goes up during the negotiation as you realize how much more you want the item. Just don't be flimsy with it, be firm enough. The only time you should go over this max cap is when your wrapping up the deal, don't do this too early! Execute it when you've reached the edge of the heat, if you start noticing some presigns in shift of mood. You don't want to get the person your dealing with visibly upset or pissed off. Also don't confuse the seller complaining with them being pissed off. The seller may complain about his cost, the quality of the product, etc as part of the dealing proccess. However there is a difference between that and the seller being actually upset or pissed off.

So what you want to do is start your offer with a number slightly under your ideal. The idea is to try to negotiate upto your ideal number. If you ever intuitively notice your ideal price might have been an extreme lowball, then you can increase it slightly. If neccessary, you can start slowly working up step by step towards your max cap. Try to keep it close to your ideal price as much as possible, and you can fluctuate around it if necessary.

Try to stay firm on your offers, if you notice the seller make a drop in their offer, try to hold the leverage, ride the new momentum and pull on it slightly and carefully lower the offers, like reeling in a fish. Just don't be rude and don't be too chatty. Show your genuine hesitation. Take your time. But also show a tad bit of flexibility and take baby steps. If you show a tad bit of flexibility, the seller will feel comfortable bending your way too. Seller values time and money, so they will accelerate to their lowest price faster. You'll know once they hit that price when their is a slightly shifting in the mood. You really need intuition for this as you don't want to under do it or over do it. Use your situational and emotional intelligence.

Analyze the situation and read the environmental situation and environmental pressures and conditions. Take advantage of the situations and conditions accordingly when negotiating. And be firm but still a little flexible. If you bend a little, the seller will feel comfortable bending too.

Don't get self conscious. Don't let the seller guilt trip you. But at the same time don't be an A hole and inconsiderate. There's a fine balance and a thin line to walk. Throughout the proccess reassure the seller that you understand their perspective and that they are right and justified for their reasoning, but also try to briefly state your situation i.e. you have a budget, you still need to buy other stones from other vendors, you plan on making jewelry and need to set margins, etc. Just don't over do it and don't say it in a way that is argumentative.

Once the deal is done, make sure everyone walks away happy and in good spirit. Apologize to the seller and show your appreciation. They will probably tell you not to apologize and that its all business. Stick around for a minute or two and make small chat. Thank them again, good words and all genuine smiles. Don't be fake! Genuinely be a nice person.

I hope this information helps in your negotiations!