It would have been easy to survey the crowds that visited Scotland's shops and malls over the last few days and assume that all was good again on the high street.

However, the sight of thousands of people spending millions of pounds can sometimes create the illusion of prosperity, particularly at Christmas. There is good news on the high street at this time of year, but there are some danger signs too.

The good news is that footfall has certainly been up in the last few days. At the Union Square shopping centre in Aberdeen, for example, it rose 9% in the week up to and including last Saturday; in the same period at the Silverburn centre in Glasgow, it was up by 5%.

These are encouraging signs, particularly after three tough years in a row for retailers in Scotland, and a difficult November in which footfall dropped sharply. However, it will be some time before we know how much of this footfall will be translated into sales and one factor that will certainly influence those sales is the increasing phenomenon of shoppers going into town to look at goods in store before going home to look for them cheaper online.

This understandably infuriates shop owners, although it will also contribute to the considerable growth in online sales. One forecast from Deloitte is that internet purchases this Christmas will be 20% higher than they were last year - not good news for stores with a physical presence on the high street (many of whom will rely on Christmas to get them through the year) but good news for the economy as a whole. However, if there is good news in those internet sales, and those Christmas crowds, it needs to be balanced by a dose of tinsel-free realism.

Many stores have been struggling to survive, and may hold on through Christmas only to fold in the new year, as happened in the first months of 2013. One sign of this instability is the fact that, like last Christmas, some chains have started their boxing day sales early in an attempt to get more shoppers in store.

The ringing tills in the last few days also mask some worrying trends for the shoppers themselves, mainly that real incomes are continuing to fall for most people. The critical question then is: if incomes are falling, where is the consumer spending we have seen in the last few days coming from? The suspicion must be that many consumers are taking on more debt so they can spend; others may be dipping into their savings.

Either way, it raises questions about shopping - and particularly shopping in the frenzied few days of Christmas -forming one of the main planks of a long-term economic recovery. The danger will always be that, when the savings and credit run out, the spending will go into reverse and the recovery will flounder.

None of this should undermine the fact that there have been promising economic signs in the stores in the last few days. Like the sharp rise in car registrations in September, it is one of the signs that the economy is continuing to recover. But it is important to remember that it is only one of them.