One significant issue highlighted is the possibility of a service replacing a user's transaction with another version that doesn't sponsor the user's transaction once it perceives the user has finished making payments. This practice could undermine the reliability of transaction sponsorship services, leaving users at risk of not getting the expected support for their transactions.

Moreover, Todd points out the risk of double-selling transaction space within a sponsor transaction. He illustrates this problem through a hypothetical scenario involving two customers, Alice and Bob, who both engage in multiple iterations with a service to secure as much fee space as they desire. However, upon attempting to broadcast their transactions, they find that their transactions conflict due to the service selling the same space to both. This situation leads to one party effectively paying without receiving the intended transaction support, highlighting a significant flaw in the current system that allows for the possibility of such conflicts.

Todd also discusses his consideration of a pay-for-signature scheme utilizing signature adaptors and a Lightning Network (LN) supporting PTLCs (Point Time-Locked Contracts) as a potential solution to these issues. Despite this, he acknowledges that this approach might not adequately address the fundamental problems of trust and efficiency in outsourced sponsorship. The complexity of designing a system that reduces reliance on trust while maintaining or enhancing transaction efficiency poses a considerable challenge.

In his quest for solutions, Todd references a related discussion focused on improving the efficiency of transaction sponsor block space. This conversation can be found in a thread at https://delvingbitcoin.org/t/improving-transaction-sponsor-blockspace-efficiency/696, which may offer further insights into strategies for enhancing transaction sponsorship mechanisms. The shared link serves as a resource for those interested in exploring more detailed discussions around optimizing the efficiency of sponsored transactions while addressing the inherent trust issues identified.