As part of the fine, Google was told to alter its search results to create a level playing field, and in September began allowing rival services to compete against Google Shopping for advertising "slots" in its search results.
However, the changes have been condemned by price comparison websites, which say they have done nothing to take power out of Google's hands.
They say Google's remedy has been inadequate because it continues to place its shopping service at an advantage in search results.
Although Google Shopping must now bid against rivals for paid-for positions in search, opponents say the auction is not fair, since Google is merely moving money from one part of the company to another.
Richard Stables, of price comparison site Kelkoo, said that 99 per cent of slots for shopping search results are still held by Google, showing the changes have done little to bolster competition.
"We're getting literally no volume, the solution is not fit for purpose," Stables said.
He is one of a number of critics urging Vestager to force further concessions from Google.
Foundem, the price comparison site that complained about Google eight years ago, is also understood to have held talks with the commissioner.
The commission is due to release a 200-page "prohibition decision" report into the fine in the coming weeks, which could lead to a host of formal complaints from price comparison sites.
Google is also due to file its first assessment of the changes with the commission at the end of January.
The company is on probation with the European Commission, which has enlisted KPMG and search engine experts Mavens to monitor its compliance.
If Google is found to be flouting the order, it can be fined up to 5 per cent of its daily turnover, around US$4.5bn ($6.54) a year, for the period in question.
In September, Google appealed against the fine.
A Google spokesman said: "The remedy we have implemented complies with the European Commission's order. Comparison shopping services now have the same opportunity as Google Shopping to show shopping ads from merchants on Google's search results pages."