Solutions segment net sales for the nine months ended September 30, 2023, decreased 9%, or $1.8 million, to $18.3 million compared to $20.1 million for the same period in the prior year. Adjusted gross billings for the Solutions segment for the nine months ended September 30, 2023 increased 10%, or $5.4 million, to $58.1 million compared to $52.8 million for the same period in the prior year. Net sales decreased while adjusted gross billings increased due to the aforementioned differences in the product mix between the two periods.
During the nine months ended September 30, 2023, the Company had two major customers that accounted for 21% and 15%, respectively, of our total net sales. During the nine months ended September 30, 2022, the Company had two major customers that accounted for 22% and 16%, respectively, of our total net sales. The Company had one major vendor that accounted for 16% of total purchases during the nine months ended September 30, 2023, and 18% of total purchases during the nine months ended September 30, 2022.
Gross Profit
Gross profit for the nine months ended September 30, 2023 increased 14%, or $5.2 million, to $43.2 million compared to $38.0 million for the same period in the prior year.
Distribution segment gross profit for the nine months ended September 30, 2023 increased 15%, or $4.5 million, to $35.5 million compared to $31.0 million for the same period in the prior year. The increase in Distribution segment gross profit was due to organic growth from our existing vendor partnerships, partially offset by higher early pay discounts and other rebates and discounts offered to our customers as a percentage of adjusted gross billings.
Solutions segment gross profit for the nine months ended September 30, 2023 increased 10%, or $0.7 million, to $7.7 million compared to $7.0 million for the same period in the prior year. This increase was driven by the aforementioned increase in adjusted gross billings compared to the same period in the prior year.
Customer rebates and discounts for the nine months ended September 30, 2023 were $9.2 million compared to $5.6 million for the same period in the prior year. Customer rebates and discounts vary based on terms of rebate and early pay discount programs offered to customers and timing of payments ultimately received from our customers.
Vendor rebates and discounts for the nine months ended September 30, 2023 were $6.1 million compared to $4.1 million for the same period in the prior year. Vendor rebates are dependent on programs offered by our vendors and in some cases reaching certain volume targets set by our vendors or meeting certain early payment programs offered by our vendors. The Company monitors vendor rebate levels, competitive pricing, and gross profit margins carefully.
Selling, General and Administrative Expenses
SG&A expenses for the nine months ended September 30, 2023 increased 28%, or $6.9 million, to $31.9 million compared to $25.0 million for the same period in the prior year. SG&A expenses were 3.7% of adjusted gross billings for the nine months ended September 30, 2023, compared to 3.4% for the same period in the prior year.
Included in SG&A expense during the nine months ended September 30, 2023 was stock compensation expense recognized of $1.8 million relating to the one-time stock grant of 35,000 shares of immediately vested Common Stock to our Chief Executive Officer. This grant was made in recognition of prior performance and as changes to his compensation arrangement from his participation in the Company’s Executive Severance and Change in Control Plan and the termination of his existing employment agreement.
The remaining increase in SG&A expenses were primarily due to increased salaries, commission and personnel costs in support of our continued investment in our infrastructure to drive future growth, including new personnel, employee training and development. The Company expects that its SG&A expenses, as a percentage of adjusted gross billings, may vary depending on changes in sales volume, as well as the levels of continuing investments to drive future growth. In addition, SG&A was impacted by increased professional service fees and other costs that are non-recurring.
Depreciation and Amortization Expense
Depreciation and amortization expense for the nine months ended September 30, 2023, increased 43%, or $0.6 million, to $1.9 million compared to $1.4 million for the same period in the prior year, primarily due to the full year