I've had a look on the internet to see if there is a difference between an official HDS and a Chinese clone, and based on the sparse information out there, the only difference is that you should not use a Chinese clone to try to update the ECU software i.e. a Chinese clone has all the same abilities but it might lose sync over the OBD port (so reading data with a Chinese clone is ok).
Based on that, and ***uming that he had an official HDS, I can only think that he may have updated the engine ECU software, and the engine then went into "learn" mode. In effect this would have reset the fuel trims, which might have helped temporarily. Note that it is only possible to "calibrate" the injectors on the Accord diesel ... to properly check injectors on a petrol engine, they need to be removed. Furthermore, AFAIK, it is only possible to check an O2 sensor by connecting a good DVM or an oscilloscope to the sensor and observing the signal.
If it were me, I would have wanted to go for a test drive with the HDS connected to observe the actual fuel trims in operation. From the fuel trims you can see if the ECU is struggling to keep the mixture at Stoichiometry ....if it is struggling, then you need to remove things to look ....if it isn't struggling, then the issue is caused by something else
It is going to be very difficult to find a paid mechanic who is able to do anything other than visually check the following
1. the spark plugs
2. the injectors (to see if they need cleaning)
3. maybe, the fuel pressure
4. possibly, the MAF sensor (to see if it needs cleaning)
5. hopefully, the O2 sensors (either out of the car, or using a DVM with the engine running)
6. definitely the brake calipers (with an ***istant on the brake pedal)
7. finally, the VC's
All of that list will take time, and time costs money.