In the final analysis, feeling satisfied that the price suits you is all that matters. However, I didn't fret because I paid only 200Y for my North Face jacket, while my roommate paid 375Y for hers. That's what makes shopping fun. Merchants will generally call after you to come back. They will want the hard currency.
Markets tend to open the same time but have more flexible closing hours.
P ack a pocket battery calculator which should come in handy when bargaining. For faster approximate calculations make up your own mini card with current exchange rates. K eep your valuables well protected. Use a neck-style or other secure bag for passports and excess money. Then, just carry a small amount of money in a concealed change purse.