Sanhedrin 25b - Lo Tachmod: With or Without Paying

The braisa lists a "chamsan" on to the list of the mishna of people who are passul for eidus m'drabonon. The gemara explains that it wasn't on the original list of the mishna because originally they thought that since money was being given, it is only אקראי בעלמא הוא, but then they saw that people were grabbing the items so they added it to the list. Tosafos is troubled why a chamsan isn't passul for eidus m'doraysa, since he is in violation of לא תחמוד. Tosafos offers two approaches:

1. Although the gemara in Baba Metzia 5b implies that people understand לא תחמוד to apply without paying, which implies that it actually applies even when money is paid, the truth is as they think that it only applies when money is not paid. Therefore, a chamsan who pays isn't in violation of לא תחמוד.

2. The implication of the gemara in Baba Metzia that לא תחמוד applies even when no money is paid, is in fact accurate. However, since people think that it only applies when no money is paid, the violator wouldn't be passul for eidus, since they don't realize that they are doing an issur.

The interpretation of our gemara is subject to these two approaches of Tosafos. According to the first approach that לא תחמוד doesn't apply when money is paid, the gemara is saying that originally since they were paying, they didn't become passul, but when they started grabbing without paying then they became passul for violating לא תחמוד. But according to the second approach that they were actually in violation of לא תחמוד even when they were paying, the gemara has to be saying that originally they were convincing the seller to sell albeit reluctantly, so there wasn't any violation of לא תחמוד, but later they were forcefully taking it without convincing the seller to sell so they were in violation of לא תחמוד even though they were paying for it.

Rashi seems to explain the gemara similar to the second approach of Tosafos, that originally they were not grabbing from the owner, rather convincing him to sell although he was never fully convinced to do so, but later they started grabbing and throwing the money in front of him.

Regardless of the approach, Tosafos holds that even if there is a d'oraysa violation of לא תחמוד, he wouldn't become passul on a d'oraysa level because people don't realize that this is a violation of לא תחמוד. This is clear from Tosafos 24b where he writes that as long as they don't realize that they are doing an issur, they wouldn't become passul m'doraysa.