The Scottish Retail Consortium's latest sales figures, published today, were described as "disappointingly weak" by sector expert David McCorquodale.
Mr McCorquodale, head of accountancy firm and SRC survey sponsor KPMG's UK retail sector practice, attributed the weakness of sales in Scotland to a competitive grocery market, mixed weather and "localised caution" among consumers when spending on bigger-ticket items.
The disappointing sales figures follow a survey earlier this week from financial services provider Scottish Friendly, which showed a sharp rise in the disposable incomes of Scots in the past three months.
The value of Scottish retail sales in May was down 1.6 per cent on the same month of last year, the SRC survey found. A survey last week from the British Retail Consortium showed the value of retail sales in the UK as a whole last month was up 2 per cent on May 2013.
SRC director David Lonsdale said: "Despite the return of shoppers to Scotland's high streets last month, the growth in footfall simply didn't filter through into an increase in the overall value of retail sales. Scottish consumers clearly remain cautious."
He cited a dip in sales of items for homes and gardens in Scotland in May. The SRC noted clothing and footwear was the only retail category to show year-on-year growth in sales value in May, although the rate of increase slowed.
Mr Lonsdale said: "Clothing and footwear retailers who offered good ranges continued to perform well off the back of new seasonal lines."
The value of non-food sales in Scotland in May was down 1.4 per cent on the same month of 2013, the survey found. However, the SRC estimated that, if online channels had been taken into account, non-food sales value in Scotland in May would have been up 0.8 per cent on the same month of last year.
Mr Lonsdale said: "Adjusted for the contribution of online retailing, non-food sales in general increased. However, shops reported that sales of items for homes and gardens dipped in May. This, coupled with continuing keen prices and promotions for food, ensured that the total growth of sales in Scotland was weaker than across the UK as a whole."
The SRC cited signs that Aberdeen and the Highlands, where the local economy is influenced by the oil industry, and Edinburgh fared better than other areas in terms of major purchases by consumers.
The value of food sales in Scotland last month was down 2 per cent on May 2013.
Mr McCorquodale said: "Discounts offered by grocers are being snapped up by cost-conscious consumers but, from the retailer viewpoint, these are depressing sales and consequently margins, and the situation is likely to persist in the short term."
Contrasting a 0.3 per cent year-on-year fall in the value of non-food sales in Scotland in the three months to May with a corresponding rise of 4.3 per cent in the UK as a whole, he added: "With the gap widening between Scotland's non-food growth in the last quarter and that of the rest of the UK, it appears that the recovery in the south-east [of England] has yet to gain strength north of the Border in terms of meaningful spend on household goods."
Highlighting the impact of weather on Scottish sales in May, the SRC said: "It was a dull month, with overall sunshine hours only 68 per cent of average, particularly for western Scotland, which had its dullest May in a series from 1929. It was also a wet month, notably in southern Scotland and Argyll, with up to twice the normal May rainfall in some areas."
The SRC noted, using the BRC's 1.4 per cent figure for annual UK shop-price deflation in May, the volume of retail sales last month in Scotland was down 0.2 per cent on a year earlier.