We provide businesses with services to reuse, recycle, and dispose of a wide variety of waste streams and recyclables generated by their operations. In addition, we have product sales and other revenue primarily from sales of products such as antifreeze and windshield washer fluid, as well as minor ancillary services.

We recognize revenue as services are performed or products are delivered. For example, we recognize revenue as waste and recyclable material are collected or when products are delivered. We recognize revenue net of any contracted pricing discounts or rebate arrangements.

We generally recognize revenue for the gross amount of consideration received as we are generally the primary obligor (or principal) in our contracts with customers as we hold complete responsibility to the customer for contract fulfillment. We record amounts collected from customers for sales tax on a net basis.

The following table presents our revenue disaggregated by source. Three customers accounted for 53% of revenue for the year ended December 31, 2019, and three customers accounted for 51% of revenue for the year ended December 31, 2018. We operate primarily in the United States, with minor services in Canada.

	Year Ended December 31,
	2019		2018
Revenue Type:
Services	$	88,841,868	$	93,524,370
Product sales and other		10,137,272		10,281,062
Total revenue	$	98,979,140	$	103,805,432

Our incremental direct costs of obtaining a customer contract are generally deferred and amortized to selling, general, and administrative expense or as a reduction to revenue (depending on the nature of the cost) over the estimated life of the customer contract. We classify our contract acquisition costs as current or noncurrent based on the timing of when we expect to recognize the amortization and are included in other assets.

As of December 31, 2019 and 2018 we had $113,750 and $7,448, respectively, of deferred contract costs. During the year ended December 31, 2019, we amortized $215,000 deferred contract costs to selling, general, and administrative expense. During the year ended December 31, 2018, we amortized $211,250 and $36,139 of deferred contract costs to selling, general, and administrative expense and as a reduction to income, respectively.

Certain customers are billed in advance, and, accordingly, recognition of related revenues is deferred as a contract liability until the services are provided and control transferred to the customer. As of December 31, 2019 and 2018, we had $19,644 and $69,473, respectively, of deferred revenue, which was classified in “Deferred revenue and other current liabilities.”