Concentration brings more fruitful results.

1, Spend 30 minutes and 15 minutes to produce the same product is different thing, obviously, the later one is doing a shoddy work, pay less attention in detail and finding product defects.
This is one way to reduce product cost.
2, Why your suppliers stopped sending you free samples? Because you’re not concentrate with them, a bit of slippery, and always thinking of better alternatives. In this way, they think its not necessary to cut product profit to minimum and pay too much attention in production.
3, The highest price is of cause too much profit that’s you can’t accept, the middle prices are too much choices, but the lowest price is too much cheating.
4, Concentration brings more fruitful results, why? When suppliers find their clients loyalty, they know their investment will not in vain, so they are willing to spend more time on product improvement and doing more things benefit to the client. 
5, When you’re asking why most suppliers don’t give price serious and prepare documents in best detail and quality? They said, because I don’t know if he could continue with me even I spend the best day and the hardest time prepare everything for him, that means even I do my best best, the final result will be in vain. That’s the best reason they don’t want to devote and you’ll always get second grade things.
6, With concentration you spend more time communicate with the same supplier of product detail, price optimization and other business opportunities. In this way, both party can understand each other very well, trust more and have better relations. Prevented business secret released to your competitors’ supplier or your client’s supplier.