In today’s world, organizations are faced with the challenge of increasingly competitive environments, which makes it necessary to establish successful, long-term relationships with customers. Customer complaints can allow an organi-zation to improve the product and service it offers and to gain its customers. Complaining customers actually want to maintain their bond with the organization. How the organization responds to a complaint can have a major impact on the customer’s post-complaint consumer behaviour, repurchase intention, and likelihood of participating in word-of-mouth activities. While complaints have traditionally been submitted through written or face-to-face communication with an organization’s staff, with Web 2.0 and forums, customers are now submitting their complaints online (Au, Buhalis & Law, 2014, pp. 249-250). Dissatisfied customers can easily express their opinions and comments about pro-ducts, services or organisations through various websites (Lee & Song, 2010, p. 1073). Electronic-based environ-ments provide consumers with the opportunity to share their experiences, ideas and knowledge on certain issues with others (Bickart & Schindler, 2001, p. 32). The purpose of the study is to evaluate the complaints on the website sikayetvar.com and to analyse the prominent themes in these complaints. To this end, the complaints against the two company/brands operating in the e-commerce and cargo/transportation sectors and with the highest number of complaints were analysed using the “case study research” meth- od on the basis of a qualitative research approach. The questions that were answered in the research are as follows: • What themes have come to the fore in the complaints against the e-commerce company? • What themes have come to the fore in the complaints against the cargo company? • What complaints have been expressed most often about the e-commerce and cargo company? • What is the distribution of complaints about e-commerce and cargo company in terms of gender? In the context of the research, the data were collected using the document analysis technique. In the analysis of the data, the MAXQDA 2020 qualitative analysis program was used. On this ground, two companies/brands were purposefully selected for the study within the scope of the sample. Accordingly, 200 complaint documents have been collected for each company since 21 February 2021. The process from the construction of the theoretical framework of the study to the analysis and interpretation of the data was carried out by three researchers. As a result of the analysis, three main themes related to the e-commerce company emerged. The themes in ques- tion were determined as “product / service problems”, “technical issues “and “customer service.” Customers frequently men- tioned “defective product sales problems”, “return problems”, “cargo problems” and “supply prob-lems” regarding the e-com- merce site as product or service problems. The numbers of coded sections of the sub-themes related to technical problems are included as “system problems and demands (51)” and “security problems (18).” It has been determined that systemic problems and demand are more frequent than security problems. The customer representative’s giving satisfactory informa- tion to the customer, taking into account the customer’s request, and the sensitivity he/she has shown in solving the problem, and moreover, showing the necessary care in building relations with the customer (such as listening, being respectful, acting politely, displaying a positive attitude) will contribute to the emergence of satisfied customers. As a result of the research, four main themes related to the cargo transportation company were identified as “not delivering the cargo to the receiver”, “customer service”, “distribution problems” and “not paying attention to the cargo.” Incorrect delivery, which constitutes the theme of not delivering the cargo or the shipment to the recipi-ent, is the most fre- quently mentioned complaint. Communication problems, which constitute the customer service theme of the cargo transpor- tation company, were the most repeated complaint with the section coded 100. Organisa-tional mistakes were repeated 12 times. Communication problems are the most common complaint against the cargo company. As a communication problem, the branch’s not answering the phone is in the first place. One of the promi-nent complaints arising from the distribution problem related to the cargo company is that the cargo or the shipment is kept in the branch. During the cargo delivery pro- cess, the loss of the cargo, its damaged delivery, or the occurrence of a deficiency in its content may lead to some grievances for the customers. E-WOM can be an important method for companies to provide feedback on products and services. Customer ser- vice refers to a service offered by companies before, during and after purchasing any product or service. In this context, cus- tomer representatives who will take part in customer services should make an effort to meet the informa-tion needed by the customer and to eliminate uncertainty and concerns.