Some dealers do not bargain at all. They don't have to because they priced fairly or think they might know someone willing to pay that price. Some will take half on coin they are tired of failing to sell. Some coins are worth every cent of the asking price and you should snap these up before I do. Some coins are not 'worth' their melt value. Your job is to learn to tell the differences TO YOU. What I think is not important unless I am the one buying or selling. If you look at my 100 favorite coins you may easily say, "Why did he want THAT?" That is good and normal. If you can't see why a coin sells for $100 or $100,000 just be glad you did not pay that for it. We all find our places, our favorite sources and our tolerances for passive aggressive dealers.
Don't talk about price and value. Just make an offer, lower than what you want to pay. Most sellers are willing to come down a bit and they may give you a counter-offer. I've learned that forthright bargaining is far more effective than beating around the bush. And don't be afraid to walk away from over-priced coins. There are more fish in the sea - literally millions of them.
I usually offer about 15-20% off, or more if I think the coin is worth way less or has been setting in the shop for a long time. If they say no, I get the coin if I really want it or I just leave it be and be patient for the next coin to come along. When I write them, it's usually brief and to the point because a lot of people don't like reading long paragraphs.
Like with any hobby buy the book first and if you can't find a book then come to a place like here and ask questions. Just like if you were building a model car, playing with radio remote control items or even playing a game. If you don't have instruction it won't be as much fun, you probably won't know much and things can go wrong. Sorry if I went on too long, but I've been there and have learned the hard way.