Trading Funds for Bitcoin Question

I would be trading poker funds or other similar funds to others for bitcoin. Those people who trade bitcoin usually ask for a percentage such as they are willing to swap bitcoin for pokerstars and want 3 or 4 or 5 percent. First off... can someone translate this to me in numbers how does that work? I done trades where i would trade $970 bank of america for $1000 pokerstars from someone... thus im buying pokerstars at 97 cents and thus they are selling poker funds for 3 percent vig as real money is always worth more than poker money.

Assuming someone wants to swap bitcoin for poker money and let say they want pokerstars + 3%... can someone translate this to me with numbers? Say i have $1000 pokerstars and want bitcoin. So they will send $970 worth of bitcoins right? At the moment 1 BTC is worth 228.34. So how it would work is when we both agree on the trade, then we use the current bitcoin price from a site such as okay bitcoin is worth $228.34 right now? Thus he would be sending me 4.25 bitcoins. Is that correct? So if i send him pokerstars, it usually takes a few minutes for the other party to receive it. But i want to know when is the price locked when doing transfers. Is it when both of us agree on trade then whatever is the current bitcoin price, then he will send the exact amount of bitcoin? Also some users say we will use bitstamp prices whereas i recall i seen others mention another site like kraken etc. I checked and prices seem to be different with all these current btc sites so which site is the main site then? Thus one site might say 1 btc is worth 250.33 but another site is 249.86 right? And if so, which one do most ppl generally choose? So basically once they send it, its pretty quick right? However when they send 4.25 btc, its almost never 4.25 btc right? Thus it might be 4.23 or 4.28 btc by the time you receive it? I believe u can only send btc amount and not dollar amount right? But even if you do dollar amt, it shouldn't matter since the btc amount would change anyways even during those 5 minutes?

Another question i have is when they send me the bitcoin, are they going to send to my coinbase account or my blockchain/multibit wallet? I currently have a coinbase acct but didn't verify my bank account yet. I was told to use blockchain or multibet/electrum for sending/receiving bitcoin and also b/c i will be transferring btc to gambling sites and thus i can't transfer directly from coinbase to it b/c coinbase will ban your acct b/c they dont like gambling transactions. So would they be sending to my blockchain or multibet/electrum then? Since if i give them my coinbase address... then theres no point right since i plan to send it to gambling site? Im a bit confused but can u even receive transfers using just coinbase from other btc users or you have to have blockchain or multibet or some type of secure hardware wallet.

Another question I have is are there anyone here that doesn't have a coinbase account and just have blockchain account or electrum/multibit only? Thus they never transfer funds to their bank account directly through coinbase and basically just trade btc a lot for poker funds or even boa? Thus not cashout directly to coinbase and dont even have a coinbase acct? Or is that extremely rare. Im curious if thats even possible if u dont plan to cashout directly to your bank acct and if you just trade btc for someones online bank transfer and its similar. Obviously having a coinbase acct is pretty essential but im wondering if theres anyone without a coinbase account.

Thanks all.