The "buy it and just return it if you don't like it" policy has become increasingly popular in recent years due to the rise of e-commerce and the desire of retailers to provide a hassle-free shopping experience for customers. However, it is difficult to predict exactly when this policy will become old and outdated as it depends on various factors.

One factor that could contribute to the decline of this policy is the increasing cost of returns for retailers. Processing returns, restocking items, and covering shipping costs can be expensive for businesses, especially if a significant portion of customers take advantage of the policy. As retailers analyze their bottom line and evaluate the impact of returns on their profitability, they may start to reconsider the generosity of their return policies.

Another factor that could influence the future of this policy is consumer behavior and expectations. As you mentioned, some shoppers have become more aware of the tactics used by retailers and may be less inclined to abuse return policies. Additionally, as people become more conscious of sustainability and the environmental impact of excessive returns, they may be more cautious about returning items they don't truly need.

It's worth noting that some retailers have already started to tighten their return policies. For example, Amazon has been cracking down on customers who abuse their return system by suspending accounts or limiting the number of returns allowed. This suggests that the trend of lenient return policies may be reaching its limits.

As for your own online selling situation, it's important to consider the balance between providing a good customer experience and protecting your business interests. While offering a flexible return policy can attract customers and build trust, you should also be mindful of the potential impact on your profitability. It's up to you to determine the right balance for your business.

In summary, the "buy it and just return it if you don't like it" policy may not disappear entirely, but it could evolve or become less prevalent in the future. Retailers will likely continue to assess the costs and benefits of such policies, while consumer behavior and expectations may also play a role in shaping the future of return policies.