Whittemore, J.

This is a petition under G. L. (Ter. Ed.) c. 79 to assess damages for the taking of real estate in Holden in September, 1953. The petitioners saved exceptions to certain rulings excluding evidence. There was error.

1. The trial judge excluded the opinion of Charles W. Bowker, Junior, of the fair market value of the petitioners’ *724 land at the time of the taking. The objection was based on the ground that Bowker’s examinations and appraisals were in August and November, 1954. There was other testimony that the physical condition of the estate was the same in 1953 as in 1954. Bowker’s general qualifications were admitted. The petitioners made an offer of proof of Bowker’s testimony of value before and after the taking, which was good practice though not essential. See Newton Girl Scout Council, Inc. v. Massachusetts Turnpike Authority, ante, 189, 199.

The acceptance by the respondent of Bowker’s qualifications meant that he had sufficient knowledge of general facts relevant to land values in Holden and sufficient experience to make his opinion of some worth, provided he was reasonably well informed about the location, appearance and condition of the petitioners’ property at the time it was taken. Inspection of property while in the same state as at the taking date is certainly, to say the least, a good way of acquiring the necessary knowledge. Under the circumstances of unchanged conditions the difference in date was without material significance. Lyman v. Boston, 164 Mass. 99, 103, 106. First National Bank v. Coffin, 162 Mass. 180, relied on by the defendant, is distinguishable.

Although the admission or exclusion of opinion testimony of this kind is largely in the discretion of the trial judge, Muzi v. Commonwealth, ante, 101, 106, and cases cited, it is manifest that there was an error of law in excluding this testimony on the ground stated.

There was no error in excluding Bowker’s opinion of the value of a portion of the land along the highway. This opinion was sought on a showing of Bowker’s greater familiarity therewith in 1953. We need not consider whether a case may arise in which evidence of the value of a part of the land would be necessary or useful to enable the fact finding tribunal to arrive at a value of the whole before and after the taking under G. L. (Ter. Ed.) c. 79, § 12. This is not such a case.

2. The petitioner John P. Ford testified on eross-exami- *725 nation .that the petitioners when they bought the property in April,-1943, paid $5,000 for it. On redirect he was asked, “What was . . . [the - sellers’] position at the time you bought it?” This was excluded and the petitioners offered to prove that “the purchase price was reduced because the sellers . . ., the man had already entered the service, and the woman was about to enter the military service . . . and . . . they therefore were anxious to dispose of the property.” The respondent having made the 1943 sale relevant under the considerable latitude allowed on cross-examination, see Whitman v. Boston & Maine Railroad, 7 Allen, 313, 318, it was open to the petitioners to show circumstances of the sale. Lawrence v. O’Neill, 317 Mass. 393, 397-398. Ham v. Salem, 100 Mass. 350, 352. The legal presumption that the sale in 1943.was fixed freely and not under compulsion which supports the admission of a sale otherwise relevant and casts on the other party the burden of going forward with evidence of compulsion, Epstein v. Boston Housing Authority, 317 Mass. 297, 300-302, does not make such evidence irrelevant as the respondent suggests. The pressure on the sellers was relevant even if it did not establish compulsion. It was a circumstance of the sale. However, the great divergence between the 1943 price and the 1953 values, as testified by a witness for the respondent (300%-400%) and as shown by other opinion evidence of the 1953 value, showed how remote and insignificant was any evidence of 1943 value, and we do not think in view of this that the exclusion of this evidence was prejudicial.

3. The qualifications of Thomas J. O’Connell, called by the petitioners, were admitted. He testified that he was in the real estate business in 1942 and a part of 1943 and was familiar with real estate values in January, February, and March, 1943; that he went into the service and was back in the business in 1953. The petitioners excepted to the exclusion of the question of how the values in Holden in those three first months of 1943 compared with the same values in the fall of 1953.

■ The 1943 value having been brought into the case by the *726 respondent it would have been within the reasonable discretion of the judge to admit this evidence but there was no prejudice for the reason stated in section 2 of this opinion.

4. Because of the error in respect of Bowker’s testimony the entry must be Exceptions sustained.