Despite the economic downturn and tough competition from the largest online retailers, sales at web-only office and business supplies retailer ReStockit.com are up more than 25% year over year through August, co-CEO David Redlich says.

ReStockit, which also sells computers, consumer electronics and restaurant supplies, competes in a market dominated by the largest e-retailers, including Amazon.com Inc., Staples Inc., Best Buy Co. Inc. and Costco Wholesale Corp.-all within the top 14 online retailers as listed in the Internet Retailer Top 500 Guide.

But with an aggressive approach to promoting products and by responding quickly to customer demand, ReStockit’s sales are up 28% year over year through August, and are on pace to hit about $18 million this year, up from $14.5 million last year, Redlich says. We see ourselves competing against the big boys because we’re nimble and flexible, he says. We’re like the little prize fighter who jabs quickly back and forth, going up against the bigger stalwart that doesn’t move as quickly.

One new technique that has hooked shoppers is a 110% price guarantee: ReStockit offers shoppers a coupon valued at 110% of the difference if they report a lower price within three days on an item similar to one purchased on ReStockit.com, Redlich says. ReStockit promotes the 110% offer across the top of its home page and authorizes customer service agents to use live chat sessions to check prices and, if warranted, immediately issue a coupon code.

To maintain profit margins amid the price discounts, ReStockit gets suppliers to agree to wholesale price rebates for hitting retail sales targets. Simply asking them to lower their prices doesn’t always work, especially if you want them to stay in business, Redlich says. The rebates help with our margins and in setting low pricing for our customers.